The introduced and invasive flora of Bermuda

The introduced and invasive flora of Bermuda | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article The introduced and invasive flora of Bermuda Alison Isabel Copeland, Wayne Dawson This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4958039/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 14 Mar, 2025 Read the published version in Biological Invasions → Version 1 posted 5 You are reading this latest preprint version Abstract Abstract Screening incoming plants for potentially invasive species is key to preventing new invasions on islands. Doing this effectively requires knowledge of plants already present and invasive in the country, and which pathways, donor regions and families have previously contributed the most invasives. As Bermuda previously lacked such a dataset, we compiled a comprehensive inventory of the native, introduced, casual, naturalized and invasive plants from historic and modern literature, herbarium records and field visits. The inventory contains updated taxonomy, pathways and dates of introduction, native geographic range, life form, and naturalization status for 1587 vascular plants from 162 families. Of these, 1424 species (89.7%) are introduced to Bermuda, while 151 (9.5%) are native. Classifying stage of invasion shows 320 species (22.5% of the introduced flora) have escaped cultivation to form casual, naturalized or invasive populations. Bermuda currently has 43 invasive plants, representing 2.7% of the total flora and 3% of the introduced flora. Among the invasive species 25 (56%) are trees and shrubs, mostly of Asian origin. Ornamental horticulture was the introduction pathway for 77% of invasive plants, emphasizing the need for further collaboration with the commercial horticulture sector and private gardeners to reduce invasion risk from ornamental plants. checklist invasion stage introduced plants island flora alien species Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction Oceanic islands are often characterised by species-poor native floras due to significant natural barriers to colonization (Sterrer et al. 2004; Weigelt et al. 2015; Moser et al. 2018). Thanks to past and present global trade and transport networks, oceanic barriers no longer protect islands from invasion because human activities remove obstacles to arrival, survival and dispersal. Today island isolation is positively associated with increased richness of introduced or naturalized plant species (Pyšek et al. 2017; Moser et al. 2018; Sánchez-Ortiz et al. 2020), and oceanic islands contain more naturalized plants than continental regions of similar size (van Kleunen et al. 2015). The islands of the wider Caribbean region have a history of habitat clearance for agriculture and natural resource exploitation as part of complex colonial trade networks (Lefroy 1879; Kairo et al. 2003; Rojas-Sandoval and Ackerman 2021; Witt 2023). The disturbed, human-dominated ecosystems on these islands have relatively low native plant species richness and high introduced plant richness, some of which are considered invasive species (Sánchez-Ortiz et al. 2020; Rojas-Sandoval and Ackerman 2021). The challenge this poses for conservation of native biodiversity and invasive species management is further exacerbated by high population densities, increasingly large-scale tourism developments, and the continued reliance on imported commodities, all of which serve to increase propagule and colonisation pressures (Essl et al. 2019; Witt 2023). The high transport connectivity between the Caribbean and the rest of the world means that invasive species introductions represent an ongoing threat to native biodiversity in the region. Bermuda has a 400-year long history of habitat disturbance and natural resource exploitation due to its mid-Atlantic location between the former colonial nations of Europe and their territories in the New World (Lefroy 1879; Hemsley 1884; Sterrer et al. 2004). Due to this geography, naturalized plants and animals deposited by passing ships pre-date Bermuda’s settlement (Lefroy 1877; Lefroy 1879; Collett 1987; Sterrer et al. 2004; Marshall et al. 2005). Until 1942 the portions of Bermuda not cleared for buildings or agriculture were densely covered in endemic Bermuda cedar Juniperus bermudiana forest (Harshberger 1905; Beard 1940; Challinor and Wingate 1971). Weeds inhabited roadsides, fields, and waste ground, comprising mainly accidentally introduced herbs and grasses from Europe and North America (Reade 1883; Lefroy 1884; Britton 1918). Several ornamental species had escaped cultivation, but only a few had established in the understory of the cedar forest (Harshberger 1905; Britton 1918; Beard 1940). Today, however, Bermuda’s fragmented woodlands often comprise a canopy of invasive broadleaved trees over a diverse understory of naturalized shrubs, vines, herbs and grasses (Sterrer et al. 2004; Marshall et al. 2005; Wolsak et al. 2018.) A single catastrophic event initiated the shift to woodlands dominated by introduced plants. Between 1944 and 1955 two accidentally introduced insects attacked the Bermuda cedar, killing 90% of the trees in the country within eleven years (Groves 1955). This event, known locally as the Cedar Blight, resulted in the complete loss of tree cover, devastation of local habitats, exposed homes and farmlands to wind and sea spray, and denuded the landscape as tourism was becoming a mainstay of the Bermudian economy (Groves 1955; Challinor and Wingate 1971; Sterrer et al. 2004). To replace the lost vegetation, a national reforestation programme began in 1949 (Groves 1955). Salt-tolerant, fast growing trees and shrubs were imported to provide crucial windbreaks (Challinor and Wingate 1971; Sterrer et al. 2004) and ornamental species from all over the world were imported to beautify the landscape (Whitney 1955; Groves 1955; Challinor and Wingate 1971; Sterrer et al. 2004). The consequence of the Cedar Blight was extreme ecosystem disturbance resulting in an unforested landscape primed for invasion. The rapid importation of a large volume of plant material, release of these plants directly onto the landscape and selection of plants with characteristics suited to the environmental conditions set the stage for nation-wide plant invasions. The appearance of the country, along with the species composition of its plant communities changed completely in the half-century following the reforestation programme (Sterrer et al 2004; Wolsak et al 2018). Today invasive species management and the prevention of new invasions are Government priorities, as highlighted by the recent passage of the Invasive Alien Species Act 2021 (Government of Bermuda 2021). Better tools are needed to improve on-island invasive species management, and to more effectively assess invasion risk from incoming plants by identifying taxa, regions and pathways most likely to contribute new invasive species. An inventory of plants already present in Bermuda and an updated list of invasive and naturalized species is needed to facilitate better management. Bermuda’s biodiversity has been well inventoried (Sterrer et al. 2004), but the information is not well reported or accessible. In this study we compiled a comprehensive checklist of plant species reported from the Bermudian literature and other sources. Using this inventory, we then aimed to: i) update the taxonomy and examine which families and genera are most represented in the introduced flora, ii) categorise the stage in the invasion process reached by each species based on barriers overcome (Richardson et al. 2000; Blackburn et al. 2011), iii) examine the life cycles and life forms of the total introduced flora and those which have escaped cultivation, iv) explore the introduction pathways and whether introductions were intentional, and v) report the native origins of the introduced flora and Bermuda’s invasive plants. Methods Study area Bermuda is an oceanic archipelago in the north-western Atlantic Ocean, located at 32.4° N and 064.8° W, and 1,052 km east-southeast of Cape Hatteras, North Carolina; the closest point of continental land. The warming influence of the Gulf Stream gives the islands a frost-free, subtropical climate, despite their temperate latitude. The islands form a J-shaped archipelago of 53.7 km 2 , with a maximum elevation of 78 m above sea level. Eight main islands are connected by bridges and a causeway, allowing free movement of people, plants, and animals along the length of the archipelago. An additional 193 islands and rocky islets are scattered in the bays and harbours, 56 of which are inhabited or were at one time (Copeland and Shailer 2011). Bermuda’s resident population of 63,779 (Department of Statistics 2018), gives it a population density of 1,188 per km 2 - one of the highest in the world. Additionally, 808,242 tourists visited Bermuda in 2019 (Bermuda Tourism Authority 2020). This density puts considerable pressure on undeveloped land, natural resources and biodiversity. Compilation of plant names Nathaniel Britton’s Flora of Bermuda (1918) is considered the most comprehensive examination of Bermuda’s plants and forms the basis of our dataset. We gathered 1304 plant names from this text. Other comprehensive 19 th century publications were consulted to augment Britton’s list, primarily the Botany of the Voyage of the Challenger Expeditions (Hemsley 1884 ), Plants of the Bermudas, or Somer's Islands (Reade 1883), and the Botany of Bermuda (Lefroy 1884). Other historic texts were consulted (Tables S3&4), but many directly copied from these four lists and added little information. After the mid-20 th century, the literature becomes more focused on ornamental plants rather than the whole flora. Of particular note are the books published by the Garden Club of Bermuda (Whitney 1955; Wardman 1971; Ogden 2002). Unpublished checklists were available for some taxonomic groups. These were usually compiled by amateur enthusiasts or for specific projects, with the palm list of Ogden (2015) being the most comprehensive. Names of native plants were gathered from Britton’s list (Britton 1918). A list of species considered invasive was compiled from GRIIS (Copeland et al. 2020) and ten other publications (Table S3). The herbarium of the Bermuda Natural History Museum at the Bermuda Aquarium, Museum and Zoo (BAMZ) was consulted between August 2020 and January 2023. Plant species considered introduced to Bermuda are separated from indigenous species in this collection. The introduced plants collection and the grass collection were examined and photographed in December 2022. Two of the largest garden centres on the island were visited in December 2022 to assess the species that are presently available for sale to the public as seeds, seedlings or established plants. The garden centres contributed twenty-nine plant names that are not found in the literature or any other sources. Some of these new taxa are artificial hybrids. During list compilation, Plants of the World Online (POWO 2023) was used to align 19 th century taxonomy with currently accepted names for families, genera and species. Older names found to be synonyms of other names in our list were combined into one record. All synonyms and alternate spellings, including misspellings found in the Bermudian literature were retained to allow searching and to maintain connections with the original record. Once the final list of plant species had been compiled, the names were standardized in R using the rWCVP package (Brown et al. 2023; R Core Team 2023), which added accepted binomial, family and author fields to the dataset, according to the World Checklist of Vascular Plants (Govaerts 2023). Two names are not recognised as synonyms by POWO, and we could not determine from other sources which accepted names they refer to; therefore, these were removed from the list before it was used for analysis. Thirty-one names given by earlier authors that Britton (1918) has treated as erroneous, doubtful or a misidentification were also removed. Thirty-six names found in the historic literature were removed because the author states that the plant did not establish, and it is not recorded in recent sources or known from the island now. Some additional names are valid but do not fit the project aims – for example six seagrasses were removed so the dataset represents terrestrial flowering plants, ferns and fern allies. Non-vascular plants were excluded. Introduction status classification All plants were assigned to one of seven introduction classes based on their indigenous or introduced status (Table 1; Tables S3 and S4). Indigenous species were placed into one of two classes, with those only found in Bermuda classed as ‘endemic’ and those with wider distribution termed ‘native’. Introduced species were classified on their success in escaping cultivation and overcoming barriers to survival, reproduction and dispersal. A classification framework (Methods S1) was created based on the concept that species must overcome barriers to move through the stages of invasion (Richardson et al. 2000; Blackburn et al. 2011). We did not consider impact when placing species into the invasive category, as impact is difficult to prove in an unstudied ecosystem like Bermuda’s plant communities. Instead, following the frameworks of Richardson et al. (2000) and Blackburn et al. (2011), we used dispersal away from human habitation, and occurrence in multiple habitats to characterise invasive species, as these can be observed with certainty. Our results should, therefore, be comparable to other studies that use these frameworks to define invasive species. Classifications were based on literature and 15 years of plant observations by the first author while employed by the Bermuda Department of Environment and Natural Resources. Any species which could not be classified due to conflicting accounts of its indigenous or introduced status were classified as cryptogenic species of undetermined origin. The resulting seven status classes were: cryptogenic, endemic, native, introduced, casual, naturalized, and invasive. Life cycle and life form We obtained life form data from the Global Inventory of Floras and Traits (GIFT: Weigelt et al. 2020), using the trait 1.2.2 ‘Growth Form’, for 1432 Bermudian species and the trait 2.1.1 ‘Lifecycle’, for 1455 Bermudian species. We identified the modal life form and life cycle category for each species and used this single category thereafter. We also downloaded life form and life cycle descriptions from the World Checklist of Vascular Plants (WCVP: Govaerts 2023) for 1462 species. Consensus life form and life cycle were then determined by cross referencing GIFT and WCVP data. For 506 species there was good agreement between GIFT and WCVP resulting in a consensus life form based on both sources. Life forms for an additional 642 species appeared just in GIFT, and 213 were determined just from WCVP. For species that did not appear in either trait database, we determined their life form from Britton (1918) or various websites (Tables S3 and S4). For 72 species no information was available, so a life form was assigned from field observations or following an internet image search. For 137 species the life form was assigned based on the family. All epiphytic and ground dwelling species in the family Bromeliaceae were assigned the life form ‘bromeliad’. The life form ‘graminoid’ was given to grasses, sedges and rushes in the families Typhaceae, Poaceae, Cyperaceae and Juncaceae. All species in Arecaceae were given the life form ‘palm’. The life form ‘fern’ was assigned to ferns and fern allies in the families Aspleniaceae, Pteridaceae, Polypodiaceae, Osmundaceae, Dennstaedtiaceae and Psilotaceae. The life form ‘cycad’ was assigned to all members of Cycadaceae and Zamiaceae. The eleven possible categories for consensus life form were: aquatic, bromeliad, cycad, fern, forb/herb, graminoid, palm, shrub, succulent, tree, and vine/climber. A consensus life cycle for 480 species was determined from agreement between GIFT and WCVP. Life cycle for an additional 919 species were determined just from GIFT, and 71 were determined just from WCVP, while those that did not appear in either database were determine from Britton (1918) or various websites (Tables S3 and S4). For 86 species no information was available, so a life cycle remained undetermined. The six possible data values for life cycle are: annual, annual or biennial, biennial, biennial or perennial, annual or perennial and perennial. Dates and pathways of introduction All casual, naturalized, or invasive species were assigned to an introduction pathway category and subcategory from the Convention on Biological Diversity’s categorization of pathways for the introduction of invasive species (CBD 2014; Table S5). Pathways were mostly determined from the literature, otherwise the most likely scenario was assigned based on previous observations and communication with Bermudian habitat managers. We added a category with value 0 named ‘unknown’ if the pathway could not be determined from the literature, communication with experts or our observations. All non-escaped introduced species were assigned the value ‘cultivated’ for pathway (Fig. 4b), and given an appropriate sub pathway (Fig.4c). Following categorization of the pathway, each species was also assigned one of six categories under the variable called ‘intentional’: accidental, probably accidental, intentional, probably intentional, unaided, or unknown (Table S5). For early intentional introductions, we were often able to find an introduction year, but for recent introductions this information is often not reported (Tables S3 & S5). For accidental introductions, we could report the year of earliest mention in the literature. In total introduction dates are reported for 285 species and inferred from first mentions in literature or first appearance in herbaria for 1142 species. Species accumulation counts (Fig. 4) assume that following first record the species continues to persist in Bermuda and is therefore added to the cumulative number over time. This of course is not always true, as species are introduced multiple times and some fail to survive one or all introduction attempts. Geographic origin We obtained the geographic origins of Bermuda’s plants using the World Checklist of Vascular Plants (WCVP: Govaerts 2023), accessed through the R package 'rWCVP' (Brown et al. 2023). Species origins at the scale of botanical continents (corresponding to Taxonomic Database Working Group—TDWG Level 1, Brummitt 2001), were extracted (August 2023). We re-coded the data so that ‘1’ represents the native range and ‘0’ the introduced range (Tables S3 and S4). Results The total Bermudian flora The inventory of Bermuda’s flora contains 1883 plant names. We removed 296 names from the dataset used for analysis, including 250 taxa with doubtful presence on the island. This left 1587 species which reflects the current state of the Bermudian flora. These 1587 plant species represent 162 plant families. The most species-rich families are Asteraceae (108 species), Fabaceae (100), Poaceae (90), Arecaceae (70) and Lamiaceae (55) (Fig. 1). The 1587 species come from 886 genera, with 570 genera represented by only one species. The most common genus is Euphorbia with 23 species, followed by Ficus (15 spp.), Agave (12 spp.) and Ipomoea (12 spp.). Introduction status Of Bermuda’s 1587 plant species, 1424 (89.7%) are introduced non-natives, while 151 (9.5%) are indigenous and 12 (0.8%) are cryptogenic species of unknown origin (Table 1). Species were classified as cryptogenic when conflicting records of its introduced or indigenous status were found in the literature, with no consensus between authors (Table S3). The indigenous flora is composed of 11 species which are considered island endemics, and 140 native species shared with North and South America and the Caribbean (Table S4). The majority (77.6%) of the 1424 plants introduced to Bermuda have not escaped cultivation, and remain present only in gardens, farmlands and landscaped situations. These 1104 species were classified as ‘introduced’ (Table S3). Additionally, 107 species are considered casual, because they have escaped cultivation but do not reproduce sufficiently to maintain wild populations. There are 170 species which have naturalized in Bermuda to form self-sustaining populations outside of cultivation. A further 43 species were classified as invasive representing 3% of the introduced plants and 2.7% of Bermuda’s total flora. These invasive species are introduced non-natives which have escaped cultivation and have formed self-sustaining and actively spreading populations (Methods S1; Table S3). They have overcome all barriers to reproduction, recruitment and dispersal (Richardson et al. 2000; Blackburn et al. 2011) and are found at multiple sites in several habitats (Sterrer et al. 2004; Marshall et al. 2005; Wolsak et al. 2018). Of the 1424 plants introduced to Bermuda, 320 species (22.5% of the introduced flora) have escaped cultivation and are considered casual, naturalized, or invasive. These will be referred to collectively as the ‘escaped species’. Table 1 Species counts in each introduction class and component percentages of the Bermudian flora Introduction Status Species count % of total Bermuda flora % of indigenous flora % of introduced flora Endemic 11 0.7 7.3 - Native 140 8.8 92.7 - Total Indigenous Species 151 9.5 100 - Introduced (not escaped) 1104 69.6 - 77.6 Casual 107 6.7 - 7.5 Naturalized 170 10.7 - 11.9 Invasive 43 2.7 - 3.0 Total Introduced Species 1424 89.7 - 100 Cryptogenic 12 0.8 - - Total Bermuda flora 1587 100 - - Introduced families and genera The introduced flora of Bermuda contains 1424 species from 152 families, with 34 families represented by a single species (Table S2). The most common introduced families are Asteraceae (98 spp.), Fabaceae (95 spp.), Poaceae (69 spp.), Arecaceae (69 spp.) and Lamiaceae (54 spp.) (Fig.1). The 107 casual species come from 48 plant families, with the Poaceae (13 spp.), Asteraceae (8 spp.), Lamiaceae (7 spp.) and Brassicaceae (6 spp.) most represented. The 170 naturalized species come from 61 plant families; of which 29 are represented in the naturalized flora by only one species (Table S2). The families with the most naturalized species are Poaceae (20 spp.), Asteraceae (15 spp.), Fabaceae (9 spp.), and Plantaginaceae (8 spp.). The 43 species classified as invasive come from 30 families, with 20 families represented by a single invasive species. The most represented families in Bermuda’s invasive flora are Ranunculaceae, Asparagaceae and Myrtaceae each with three invasive species (Table S2). Among Bermuda’s invasive families Petiveriaceae stands out as it does not contain any indigenous species, and the two introduced species from this family, Rivina humilis and Trichostigma octandrum , are both invasive. The 320 species that have escaped captivity to become casual, naturalized, or invasive, all together represent 229 genera from 82 families. The most frequently escaped families are Poaceae (34 spp.), Asteraceae (25spp.) and Fabaceae and Lamiaceae with 12 species each. The genus with the most escaped plants is Euphorbia with 7 species, followed by Oxalis (5 spp.) and Erigeron, Ipomoea and Ranunculus with 4 species each. The 43 invasive species represent 35 genera, with three species of Asparagus and Clematis , and two species of Abutilon , Cardiospermum, Heptapleurum and Pittosporum . The 1104 introduced species belong to 139 plant families. The most represented families among these cultivated species are Fabaceae (83 spp.), Asteraceae (73 spp.), Arecaceae (63 spp.), Lamiaceae (42 spp.) and Solanaceae (37 spp.). The 1104 introduced but not escaped species come from 662 genera, with 450 genera having a single introduced species. The most represented is Ficus with 14 species, followed by Euphorbia (11 spp.), Agave (10 spp.), Begonia, Senna and Solanum (9 spp. each), and Salvia (8 spp.). Comparison of the escaped flora with those remaining only in cultivation shows that Asphodelaceae, Zingiberaceae and Annonaceae are the families with the most species introduced to Bermuda but failing to naturalize, with 11, 10 and 8 species respectively. The genera that are most widely introduced but have not escaped include Senna and Solanum with 9 introduced species each, and Clerodendrum , Erythrina and Hibiscus with 7 species each. Life forms Most of the 1424 plants introduced to Bermuda are herbs/forbs (40%) followed by trees (18%), shrubs (17%), vines/climbers (7%), graminoids (5%), succulents (5%) and palms (5%). Non-woody life forms make up the majority of the escaped flora which is 54% forbs and 12% graminoids (Fig. 2). Forbs comprise 61% of both casual and naturalized species, followed by graminoids (12% of casual species and 14% of naturalized species). In contrast, woody life forms make up much of the invasive flora with 33% being trees and 23% shrubs followed by 6% vines/climbers. Bermuda’s 43 invasive plants display seven life forms, including 4 forbs, 4 ferns, one grass, 9 vines, one palm, 10 shrubs and 14 trees (Fig. 2; Table S3). Life cycles Perennial life cycles dominate the introduced flora, with 1112 perennial species (78%). Among the 320 escaped species, 25% are annuals and 55% are perennials. The remainder are some combination of annual, biennial or perennial as multiple types of life cycle were reported in the sources consulted (Table S3). Perennial life cycles are most dominant among the invasive species also, with only two definite annuals ( Abutilon theophrasti and Cardiospermum halicacabum ) and Cardiospermum grandiflorum classed as ‘annual or perennial’. The remaining 40 invasive species (93%) were perennial. Native range of the introduced flora Bermuda’s introduced flora contains plants from all nine continents in the Taxonomic Database Working Group (TDWG) continental scheme (Brummitt 2001; Govaerts 2023). Some species were native to five or six TDWG continents, making comparative percentages uninformative. The major sources of introduced species are Temperate Asia (352 spp.), Southern America (336 spp.), Northern America (322 spp.), Tropical Asia (282 spp.) and Africa (278 spp.). The 320 plants that have escaped cultivation also originate from all nine continents (Fig. 3; Table S3), with Temperate Asia (117 spp.), Africa (99 spp.) and Northern America (90 spp.) as the major sources. The 43 invasive species are native to eight continents, excluding Antarctica. Again, Temperate Asia is the most represented potential source, supplying 18 invasive species, followed by Tropical Asia and Africa (12 spp. each), Southern America (10 spp.) and Australasia (7 spp.) (Fig. 3; Table S3). We grouped the nine TDWG botanical continents into broader areas that species were native to, giving five combinations of continental origins (Table 2). We examined the conversion rate of total species in all introduced classes to invasive species. Oceania (includes Australasia, Antarctica, and Pacific) had the highest conversion rate (8.2%) despite the fewest introductions originating from this part of the world. Asia (Temperate Asia and Tropical Asia) and Africa had rates roughly half as high, with 4.7% and 4.3% respectively. The Americas (Northern and Southern America) had a low conversion rate despite a large number of introductions from this region (Table 2). European species had the lowest conversion rate with only 1% of introductions becoming invasive. Table 2 Conversion rates of introduced species into invasive species by grouped continents of origin Native Origin Invasive in Bermuda All Introduced to Bermuda Conversion Rate (%) Oceania 12 147 8.2 Asia 30 636 4.7 Africa 12 279 4.3 Americas 16 658 2.4 Europe 2 199 1.0 Introduction pathways of casual, naturalized and invasive flora The majority of Bermuda’s 1424 introduced plants were brought to the island intentionally (88%), while 11% were accidental introductions, and for 1% the introduction type could not be determined from the literature. For the 320 species in the escaped flora, 53% were intentional introductions, while 46% were accidental and 1% were unknown (Table S5). Among invasive species, 93% were intentionally introduced, while 7% were accidentally introduced. The majority of casual and naturalized plants arrived as contaminants in imported goods prior to 1918. These historic contaminated imports account for 45% of casual species and 42% of naturalized species introductions (Table S5). The introduction of plants as contaminants is probably under-represented by these figures, as the true number of plants that arrived but did not establish, or were not reported, cannot be known. Escape from cultivation of plants imported for ornamental purposes accounted for 28% of casual species and 29% of naturalized species. Plants imported for agriculture, particularly fodder grasses, account for 10% of naturalized species introductions. Of Bermuda’s 43 invasive species, 36 species (84%) have escaped from cultivation, with three introduced as fruit trees, and 33 species (77% of the invasive flora) for ornamental purposes. The three trees with edible fruits are the Surinam cherry Eugenia uniflora , loquat Eriobotrya japonica and guava Psidium guajava . Another four invasive species were intentionally released into coastal habitats for erosion control or as windbreaks, namely the Australian whistling pine Casuarina equisetifolia , Madagascar olive Noronhia emarginata , beach naupaka Scaevola taccada and seaside creeping daisy Sphagneticola trilobata. Introduction date or earliest record The majority of Bermuda’s introduced plants arrived between about 1830 and 1930 (Fig. 4). The sharpest increase in the introduction of species that were released from, or escaped cultivation occurred between about 1880 and 1918 (Fig.4b). Of Bermuda’s 43 invasive species, 26 were already present when Dr Britton surveyed Bermuda’s flora between 1905 and 1912 (Britton 1918; Table S3). From the mid-20 th century onward the rate of introduction of escaped species flattens off, while total introductions continue to increase (Fig. 4a and 4b). New pathways of introduction appear in the late 20 th century, with the first record of a casual species attributed to transport on the wheels of an airplane appearing as a herbarium specimen in 1981 (Fig 4b). The introduction of two naturalized plants predate settlement, having been recorded on the islands in 1593 (Fig. 4a; Lefroy 1884; Collett 1987; Sterrer et al. 2004). Once the British arrived in Bermuda in 1609 a low volume of plant introductions began, with little increase for 200 years (Fig.4a). Bermuda’s colonial governor from 1871 to 1877, Sir John Henry Lefroy was a keen botanist who exchanged plants with botanical gardens in the United States, and Europe (Lefroy 1884; Wolsak et al. 2018) and was responsible for introducing more species to Bermuda than any other person (Marshall et al. 2005). The activities of Governor Lefroy resulted in a cluster of well-documented introductions in the 1870’s (Fig.4a; Reade 1883; Lefroy 1884; Britton 1918). Other large increases in first mentions of introduced plant species result from the publication of major botanical works in 1883, 1884, 1918, 1933 and 1971 (Reade 1883; Hemsley 1884; Lefroy 1884; Britton 1918; Baker 1933 in Jones 1986; Wardman 1971). Discussion The 1587 indigenous and introduced plants reported in our inventory represent Bermuda’s first checklist of accepted plant names with modern taxonomy and a standardized classification of their introduction status, life form, native range and date of first record. Our analysis of the inventory indicates that within the Bermudian flora introduced species outnumber indigenous species 9:1, and escaped introductions outnumber indigenous plants 2:1 (Table 1). The introduced Bermudian flora comprises 1424 species, 320 (22.5%) of which are found outside of cultivation, including 43 (3%) that have become invasive. Here, we discuss these findings in the context of Bermuda’s economic development stages, present and historic landscapes, and we compare Bermuda to patterns in naturalized floras globally and on other islands. Economic development stages and plant introductions Bermuda has passed through various stages in its socioeconomic development since the islands were permanently settled. Plants were imported at each stage through varying trade and transport links to meet various goals (Collett 1987; Sterrer et al. 2004), which influenced both introduction pathways and propagule pressure, and in turn dictated the potential for invasion (Essl et al. 2019). The British settled Bermuda in 1609 and a permanent colony was established in 1612 (Lefroy 1877). The earliest introductions were crops and medicinal plants critical to survival of the new colony, which were sent from Europe and are well reported in the colonial records (Lefroy 1877; Lefroy 1879; Collett 1987). Two naturalized species, papaya Carica papaya and the European olive Olea europaea have the earliest recorded mentions in the literature from 1593 (Fig. 4a), giving a current residence time of 430 years (Collett 1987; Sterrer et al. 2004). Lefroy (1884) reports that Olea europaea was already “naturalized, probably from seeds sown by the crews of Spanish vessels visiting the islands or wrecked on them in the sixteenth century” when the first colonists arrived in 1609. The next oldest naturalized species is the common fennel Foeniculum vulgare introduced in 1616 as seeds sent from Europe (Lefroy 1884; Collett 1987). Today fennel is naturalized on grassy hillsides and among sand dunes along the South Shore. The earliest reported non-edible introductions are, the wild indigo Indigofera suffruticosa and castor oil plant Ricinus communis both introduced prior to 1623, and cotton Gossypium herbaceum introduced in 1624, all of which were imported as cash crops for export (Lefroy 1884; Hemsley 1884; Collett 1987). European colonies in the New World sought to develop all potential commercial ventures, so plants arriving at this time were intended to generate profits. Many new plants were being discovered by European explorers in the mid-17 th century and these were sent to the colonies for trial as commercial enterprises (Lefroy 1879; Lefroy 1884; Collett 1987; Sterrer et al. 2004). The earliest mention of a non-agricultural plant is the pasture weed Sida acuta . On November 10 th , 1669 the Governor Sir John Heydon issued a notice to all tenants that they are to pull up the wireweed or risk forfeiting their land for neglect of it (Lefroy 1879). Governor Lefroy has made a footnote on this record, reporting Sida acuta was “still a great pest” over 200 years later (Lefroy 1879). From the early years of the Bermuda colony up until the 1930’s hay was imported from North America to feed the island’s horses (Lefroy 1884; Sterrer et al 2004) providing an important pathway for weeds to enter as contaminants (Fig. 4b and 4c). It is likely several naturalized plants entered the island this way, both native North American species, and those European weeds with naturalized populations in eastern North America. Bermuda had primarily a trade economy from the 17th to 19 th century, during which Bermudian seafarers travelled widely and brought home many plants they encountered abroad, which were planted in a ‘trial and error’ fashion (Reade 1883; Lefroy 1884); a practice which continued into the 20 th century (Britton 1918; Jones 1986). Governor Lefroy laments at length that ornamental horticulture, particularly flower gardening, was not widely undertaken by Bermudians in the 1870’s, a situation he began to remedy with the import of seeds and plants from all over the world and professional gardeners from Britain (Lefroy 1884). Attitudes to ornamental plants did change in this period, with most of Bermuda’s total plant species, and ornamentals in particular, introduced between 1830 to 1930 (Fig. 4c). Landscaping of public spaces began in this period (Reade 1883; Britton 1918), including the establishment of the Public Gardens in 1898, which would become the Bermuda Botanical Gardens in 1958 (Department of Agriculture 1961). As Bermuda transitioned to a service economy based on tourism in the 20 th century, the interest in ornamental plants grew (Department of Agriculture 1961; Sterrer et al. 2004). Legacy of the Cedar Blight In the years immediately following the Cedar Blight of the 1940s, Bermuda’s landscape changed from one covered with relatively few indigenous species to one dominated by a diversity of introduced plants (Groves 1955; Challinor and Wingate 1971; Sterrer et al. 2004; Wolsak et al. 2018). The reforestation programme that began in 1949 has been acknowledged as responsible for the spread of now-invasive plants (Sterrer et al. 2004), however, we found relatively few introduction dates or first mentions of escaped species around 1949 (Fig. 4a). This suggests that although the numbers of plants being imported, propagated and planted at that time may have been high, few new species were being added to the flora. It is likely increased propagule pressure from species already present, combined with the arrival of new seed-dispersing birds and a newly barren landscape, triggered a population expansion for many planted species. The reforestation programme involved planting imported trees, palms and shrubs along roadsides, on golf courses, on the islands of Hamilton Harbour and on all Government-owned land (Groves 1955; Challinor and Wingate 1971; Sterrer et al. 2004). Early in the programme, plantings suffered considerable losses due to wind and drought, demonstrating the need for hardier plants and the establishment of good windbreaks (Groves 1955). It is likely this focus on selecting woody species suited to Bermuda’s harsh environmental conditions that precipitated their current dominance of the invasive flora. Trees and shrubs represent only 35% of the introduced flora, and only 18% of escaped species, but make up 56% of the invasive flora (Fig. 2). The reforestation programme facilitated the release of these salt-tolerant and wind-adapted species directly into the environment on a country-wide scale, which hastened their advancement along the invasion stage continuum. Considerable government funds were spent on these planting schemes (Groves 1955). Ironically, a substantial amount is now spent each year on invasive plant and habitat management and roadside weed control as a legacy of the Cedar Blight. Comparing Bermuda’s flora to other islands Our inventory revealed a high proportion of introduced species (89.7%) in the Bermudian flora compared to just 9.5% indigenous plants. This proportion is higher than reported for other oceanic islands such as the Azores, which host 1002 taxa that are 69% introduced and 31% indigenous (Silva and Smith 2004). Bermuda also has a high proportion of naturalized species compared to indigenous ones. In a comparison of island floras across the globe, Essl et al. (2019) reported that 26% of the islands examined had more naturalized than native species. With 170 naturalized species to 151 natives, Bermuda fits within this minority. There are several patterns in Bermuda’s naturalized and invasive flora that are consistent with reported global patterns. These include ornamental horticulture as the primary pathway of introduction of invasive species (Guézou et al. 2010, Rejmánek 2014; van Kleunen et al. 2018; Rojas-Sandoval and Ackerman 2021), and thus intentional introduction being responsible for the majority of invasive species (Silva and Smith 2004; van Kleunen et al. 2018; Rojas-Sandoval and Ackerman 2021). In addition, species from Asia are well represented in the naturalized flora of Bermuda reflecting strong representation among naturalized species globally (van Kleunen et al. 2015; Pyšek et al 2017). Worldwide, islands also have more naturalized woody species than annual herbs (Pyšek et al 2017), a pattern that Bermuda adheres to. Comparing families At the global scale the naturalized flora is dominated by the Fabaceae, Poaceae and Asteraceae families (Pyšek et al. 2017), a trend that also appears at the regional scale in the West Indies (Rojas-Sandoval and Ackerman 2021) and Central America (Rojas-Sandoval et al. 2023), and among island groups such as the Galapagos (Guézou et al. 2010), and Puerto Rico and the Virgin Islands (Rojas-Sandoval and Acevedo-Rodríguez 2015). Bermuda’s introduced and naturalized flora is also dominated by Asteraceae, Fabaceae and Poaceae, however these families are not well represented in the invasive flora (Fig.1). Bermuda has only two Asteraceae classified as invasive, one Poaceae and one Fabaceae (Tables S2 & S3). This departure should be subjected to future study. It is likely a result of our strict application of the term ‘invasive’ only to plants widely dispersed into multiple wild habitats, while others consider agricultural and garden weeds as invasive (e.g. Rojas-Sandoval and Acevedo-Rodríguez 2015). For example, we classified Cenchrus purpureus as naturalized but not invasive (Table S3) because although it is dominant on the edge of freshwater marshes where it was historically planted as fodder, it has not dispersed away from these points of introduction into other habitats. Cenchrus purpureus does appear on invasive species lists for other islands such as Cuba (Oviedo Prieto and González-Oliva 2015), Puerto Rico (Rojas-Sandoval and Acevedo-Rodríguez 2015), and the Virgin Islands (Rojas-Sandoval and Acevedo-Rodríguez 2015). Similarly, many Asteraceae that appear as agricultural weeds in Bermuda were classified as naturalized since farmland is not extensive, and therefore these plants are not widespread. The palm family Arecaceae is an important source of potentially invasive plants in tropical regions, with a high risk of spread through bird dispersal of species with fleshy fruits (Rejmánek 2014). Palms were the fourth most introduced family in the Bermudian flora (Fig. 1; Table S2), due to the low native palm diversity (one endemic species only) and the popularity of palms in ornamental horticulture, particularly for tourism developments. Thus far Bermuda has only a single invasive palm, the Chinese fan palm Livistona chinensis , however naturalized populations of Phoenix reclinata and Ptychosperma elegans have appeared in natural habitats in recent years which may continue to persist and spread in the future. Comparing life forms Although herbs and forbs form the largest proportion of Bermuda’s introduced flora (40% of introduced species), they represent only 9% of the invasive flora (Fig. 2). This is in contrast to the regional pattern within the West Indies where herbs comprise the largest segment 29% (Rojas-Sandoval and Ackerman 2021) to 31% (Rojas-Sandoval et al. 2017) of the invasive flora. As with families, this discrepancy is likely due in part to the way we defined invasive species and life forms. Ruderal and agricultural habitats are important for invasive plants in the West Indies (Rojas-Sandoval et al. 2017). As neither ruderal nor agricultural land is extensive in Bermuda, weeds of these habitats, which are often herbaceous, did not meet the dispersal into multiple habitats criteria in our framework (Methods S1). Also, we used the value ‘ferns’ as a separate life form, comprising an additional 9% of Bermuda’s invasive flora (Fig. 2), while other studies did not separate ferns from other herbaceous life forms (Rojas-Sandoval et al. 2017; Rojas-Sandoval and Ackerman 2021). The poor representation of herbs in Bermuda’s invasive flora is also likely a reflection of lower propagule pressure compared to woody life forms. Comparing pathways A review of invasive species across 18 Caribbean island groups showed that 18% were unintentional introductions, while 82% were intentionally introduced (Rojas-Sandoval and Ackerman 2021). Bermuda’s invasive species broadly follow this regional introduction pattern, with 7% accidental and 93% intentional introductions, suggesting that biosecurity measures aimed at intentional imports of plant material and seeds should be prioritized over those to prevent stowaways and contaminants. Ornamental horticulture is a significant pathway of introduction for naturalized and invasive plant species globally (Rejmánek 2014; van Kleunen et al. 2018), regionally within the wider Caribbean (Rojas-Sandoval et al. 2017; Rojas-Sandoval and Ackerman 2021) and on other oceanic archipelagos such as the Galapagos (Guézou et al. 2010) and the Azores (Smith and Silva 2004). As 77% of Bermuda’s invasive plants also arrived for ornamental purposes, the need for improved regulation of both commercial and private imports of ornamental plants is apparent. Deliberately introduced, woody life forms, particularly those producing edible fruit, are overrepresented in the naturalized floras of islands globally (Pyšek et al. 2017), a pattern which Bermuda follows. The recent covid-19 pandemic has increased awareness of Bermuda’s reliance on imports and resulting lack of food security. This has made curbing the commercial sale and private distribution of invasive plants that produce edible products particularly problematic. The availability of seeds from online retailers has widened the pool of what is available to Bermudian home gardeners and the island’s commercial horticulture sector. Therefore, the risk of a new invasive plant arriving is probably very high. Donor regions Bermuda’s native flora contains Caribbean species at the northern limits of their range, overlapping species shared with southeastern North America (Hemsley 1884; Britton 1918; Groves 1955; Sterrer et al. 2004), so it is not surprising to find plants from both tropical and temperate continents naturalizing under these conditions. Asia, particularly temperate Asia, is the largest donor of naturalized plants to other regions of the world (van Kleunen et al. 2015; Pyšek et al 2017). Accordingly, temperate Asia is the most important donor to Bermuda’s flora, supplying the most invasive species (18 spp.), the most escaped species (117 spp.) and the most introduced species (352 spp.). The Southern hemisphere continents are underrepresented as donors of naturalized plants at the global scale (van Kleunen et al. 2015) but this is not the case for Bermuda’s invasive flora, where South America, Africa and Australasia are well represented (Fig. 3). Limitations of this study and areas for future research Synthesizing information from historic texts, particularly those not based on direct observation by the authors (eg. Hemsley 1884) introduces a risk of reporting error. Similarly, the use of data from non-scientific sources and unconfirmed reports from non-specialists introduces the risk of mis-identification of species. By removing doubtful names at the start of the analysis, we are confident that we minimized these sources of error as much as possible. Our inventory has identified several introduced and invasive plants that need further expert verification, as we suspect they are still mis-identified. We anticipate that following revision by family or genera experts the names and numbers of invasive and naturalized species in this dataset may change. Bermudian resources for identifying Poaceae in particular are lacking, and given the importance of this family in both the native and naturalized floras (Fig.1), this should be addressed as a priority. Preparation of this inventory did not involve any study-specific field surveys of naturalized or invasive vegetation, so we also anticipate new field data will improve our plant list and future assessment of species invasion stages. Equally importantly, any casual or introduced species that are no longer present can be noted as such, although this is hard to verify, particularly as known casual populations are not monitored. Future work should investigate impacts of invasive plants following field surveys, as we made no attempt to incorporate impact into our classification. Regardless of these limitations our inventory is an important baseline and provides a Bermuda data point and additional oceanic island data point for global studies. Improving representation of the introduced flora in national herbarium collections should also be a priority for future work. Of the 273 sheets we examined at the Bermuda Natural History Museum, the indigenous, naturalized and invasive flora were well represented, while only 53 introduced species that remain in cultivation were present. Expanding the collection will facilitate other botanical studies, allow confirmation of species identity by experts and aid future identification of new naturalized populations of represented plants. Implications for risk assessments When Bermuda’s State of the Environment Report was commission 20 years ago it was noted that “not all policy-makers or members of the public share the view that invasive species negatively impact biodiversity” (Marshall et al. 2005) and sadly little has changed in this regard. Support for restrictions on plant sales and cooperation with the risk assessment process for imports is low. By quantifying how dominated Bermuda’s flora is by introduced species and highlighting that intentional introduction of ornamental plants has resulted in most of Bermuda’s problematic invasives, we hope to demonstrate the extent of the problem to the horticulture sector, policy makers and the public. Our inventory will be a resource for those undertaking risk assessments as well as horticulturalists seeking indigenous species or non-naturalized introductions for their planting projects. Conclusion Severe habitat degradation during the 20 th century, followed by active reforestation with introduced species has left Bermuda with a substantial invasive plant problem (Sterrer 2004; Marshall et al. 2005; Wolsak et al. 2018; Copeland et al. 2020). By creating this inventory of the Bermudian flora, and developing a standardized invasion stage classification (Methods S1), we have captured the current state of this problem and its origins. Future reapplication of this invasion stage classification will allow new introductions to be tracked and emerging naturalized and invasive species to be identified, which should allow timely mobilization of resources to address them. Additionally, by demonstrating that ornamental horticulture was responsible for the introduction of most invasive plants, we hope to encourage greater cooperation with risk assessments and biosecurity policies. Declarations Acknowledgements The authors would like to thank the reviewers for their time and helpful comments. AC is supported by a Durham Doctoral Scholarship from the Faculty of Science, Durham University, and wishes to thank the Garden Club of Bermuda for additional support. We also acknowledge the assistance of the Bermuda Government, Department of Environment and Natural Resources. Author contributions AC compiled the species list, undertook data analysis and wrote the manuscript. WD advised on data collation, preparation, analysis and presentation, and edited the manuscript. Competing interests The authors have no conflicts or competing interests Supplemental material S1. Methods: Classification framework for invasion stage of introduced species. S2. Table of number of species per family across the seven introduction status classes. S3. Table of status, life form, life cycle and native origin for introduced, casual, naturalized, invasive and cryptogenic species. S4. 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Brittonia, 70: 257-275. https://doi.org/10.1007/s12228-017-9509-x Supplementary Files CopelandandDawsonCoverLetter.docx ESM1classificationofinvasivestatus.docx ESM2speciesperfamilyandinvasionstage.xlsx ESM3introducedfloraofBermuda.xlsx ESM4indigenousfloraofBermuda.xlsx ESM5introductiondatesandpathwaysescapedflora.xlsx Cite Share Download PDF Status: Published Journal Publication published 14 Mar, 2025 Read the published version in Biological Invasions → Version 1 posted Reviewers agreed at journal 17 Sep, 2024 Reviewers invited by journal 13 Sep, 2024 Editor invited by journal 31 Aug, 2024 Editor assigned by journal 31 Aug, 2024 First submitted to journal 22 Aug, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4958039","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":353590536,"identity":"2cb46a3d-d2d4-45a9-bf0d-7977975a955d","order_by":0,"name":"Alison Isabel Copeland","email":"data:image/png;base64,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","orcid":"https://orcid.org/0000-0001-8549-5054","institution":"Durham University","correspondingAuthor":true,"prefix":"","firstName":"Alison","middleName":"Isabel","lastName":"Copeland","suffix":""},{"id":353590537,"identity":"2fb239ed-50b4-4e4b-b471-1a34d3859d9a","order_by":1,"name":"Wayne Dawson","email":"","orcid":"","institution":"University of Liverpool Institute of Infection Veterinary and Ecological Sciences","correspondingAuthor":false,"prefix":"","firstName":"Wayne","middleName":"","lastName":"Dawson","suffix":""}],"badges":[],"createdAt":"2024-08-22 12:27:26","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4958039/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4958039/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10530-025-03559-8","type":"published","date":"2025-03-14T15:57:23+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":66344730,"identity":"2c42241a-4171-4120-9cf5-dc5d5ea0c533","added_by":"auto","created_at":"2024-10-10 16:35:14","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":44387,"visible":true,"origin":"","legend":"\u003cp\u003eThe top ten most species-rich families in the Bermudian flora\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4958039/v1/e8b2367fd2bba9ee97728b53.png"},{"id":66344727,"identity":"fd78e9bb-299b-4536-9a7f-4bc2746f6044","added_by":"auto","created_at":"2024-10-10 16:35:14","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":53475,"visible":true,"origin":"","legend":"\u003cp\u003eThe ten life forms of Bermuda’s 320 escaped plant species\u003c/p\u003e","description":"","filename":"f2.png","url":"https://assets-eu.researchsquare.com/files/rs-4958039/v1/7543a738fe3cb787dae395ae.png"},{"id":66345347,"identity":"dbed84e8-df33-49b3-b44d-16702d83025d","added_by":"auto","created_at":"2024-10-10 16:43:14","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":71057,"visible":true,"origin":"","legend":"\u003cp\u003eContinents of origin of Bermuda’s introduced plant species. NB. The sum of species across continents is greater than the total number of introduced species because most species are native to more than one continent\u003c/p\u003e","description":"","filename":"f3.png","url":"https://assets-eu.researchsquare.com/files/rs-4958039/v1/0bbca00f81708114eedb4235.png"},{"id":66344732,"identity":"6685c83b-d60e-4d07-9fae-33cf70ff1c01","added_by":"auto","created_at":"2024-10-10 16:35:14","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":99726,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea) \u003c/strong\u003eThe cumulative number of introduced plant species (triangles) and casual, naturalized or invasive species (circles) present on Bermuda from 1593 to 2022. Publication dates of major\u003cstrong\u003e \u003c/strong\u003ebotanical works are indicated\u003cstrong\u003e b) \u003c/strong\u003ethe cumulative number of species introduced by six pathways\u003cstrong\u003e c) \u003c/strong\u003ecumulative the number of species introduced by eight sub pathways\u003c/p\u003e","description":"","filename":"f4.png","url":"https://assets-eu.researchsquare.com/files/rs-4958039/v1/0411611d431374cc6f713c1a.png"},{"id":78689968,"identity":"313a2839-b447-4507-8c27-7066939c1f79","added_by":"auto","created_at":"2025-03-17 16:13:57","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":962247,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4958039/v1/f0595e3d-ea97-47ee-a44f-d86fe4e1bc51.pdf"},{"id":66345592,"identity":"e5bf63a3-182b-474b-8ffd-3cb06249e9b9","added_by":"auto","created_at":"2024-10-10 16:51:14","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":29779,"visible":true,"origin":"","legend":"","description":"","filename":"CopelandandDawsonCoverLetter.docx","url":"https://assets-eu.researchsquare.com/files/rs-4958039/v1/4527c0536c9027ce6f5a82f0.docx"},{"id":66344731,"identity":"0b87eaf8-c31e-429f-baf9-939525c9ec0d","added_by":"auto","created_at":"2024-10-10 16:35:14","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":19474,"visible":true,"origin":"","legend":"","description":"","filename":"ESM1classificationofinvasivestatus.docx","url":"https://assets-eu.researchsquare.com/files/rs-4958039/v1/2cf64a5e3384bf30fabb3726.docx"},{"id":66345349,"identity":"8dc05f31-11fc-4f78-83e6-d2efafe5d479","added_by":"auto","created_at":"2024-10-10 16:43:14","extension":"xlsx","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":21902,"visible":true,"origin":"","legend":"","description":"","filename":"ESM2speciesperfamilyandinvasionstage.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-4958039/v1/966c50bd5cc92122bd58aa5c.xlsx"},{"id":66344734,"identity":"02231e56-9915-40ab-95f6-77c826ff42d4","added_by":"auto","created_at":"2024-10-10 16:35:14","extension":"xlsx","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":242100,"visible":true,"origin":"","legend":"","description":"","filename":"ESM3introducedfloraofBermuda.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-4958039/v1/4cd30eac95ccf8223a79038f.xlsx"},{"id":66345350,"identity":"993f7363-f69e-47a7-8f96-157ad23ee7ee","added_by":"auto","created_at":"2024-10-10 16:43:14","extension":"xlsx","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":40307,"visible":true,"origin":"","legend":"","description":"","filename":"ESM4indigenousfloraofBermuda.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-4958039/v1/a30e20f76cf25625e6ad409f.xlsx"},{"id":66344735,"identity":"c0ec6834-ab84-4cea-ba33-4c31e322bb3c","added_by":"auto","created_at":"2024-10-10 16:35:14","extension":"xlsx","order_by":6,"title":"","display":"","copyAsset":false,"role":"supplement","size":49825,"visible":true,"origin":"","legend":"","description":"","filename":"ESM5introductiondatesandpathwaysescapedflora.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-4958039/v1/b215ce012a3d8b3524eabbed.xlsx"}],"financialInterests":"","formattedTitle":"The introduced and invasive flora of Bermuda","fulltext":[{"header":"Introduction","content":"\u003cp\u003eOceanic islands are often characterised by species-poor native floras due to significant natural barriers to colonization (Sterrer et al. 2004; Weigelt et al. 2015; Moser et al. 2018). Thanks to past and present global trade and transport networks, oceanic barriers no longer protect islands from invasion because human activities remove obstacles to arrival, survival and dispersal.\u0026nbsp;Today island isolation is positively associated with increased richness of introduced or naturalized plant species (Py\u0026scaron;ek et al. 2017; Moser et al. 2018; S\u0026aacute;nchez-Ortiz et al. 2020), and oceanic islands contain more naturalized plants than continental regions of similar size (van Kleunen et al. 2015).\u003c/p\u003e\n\u003cp\u003eThe islands of the wider Caribbean region have a history of habitat clearance for agriculture and natural resource exploitation as part of complex colonial trade networks (Lefroy 1879; Kairo et al. 2003; Rojas-Sandoval and Ackerman 2021; Witt 2023). \u0026nbsp;The disturbed, human-dominated ecosystems on these islands have relatively low native plant species richness and high introduced plant richness, some of which are considered invasive species (S\u0026aacute;nchez-Ortiz et al. 2020; Rojas-Sandoval and Ackerman 2021). The challenge this poses for conservation of native biodiversity and invasive species management is further exacerbated by high population densities, increasingly large-scale tourism developments, and the continued reliance on imported commodities, all of which serve to increase propagule and colonisation pressures (Essl et al. 2019; Witt 2023). The high transport connectivity between the Caribbean and the rest of the world means that invasive species introductions represent an ongoing threat to native biodiversity in the region.\u003c/p\u003e\n\u003cp\u003eBermuda has a 400-year long history of habitat disturbance and natural resource exploitation due to its mid-Atlantic location\u0026nbsp;between the former colonial nations of Europe and their territories in the New World (Lefroy 1879; Hemsley 1884; Sterrer et al. 2004).\u0026nbsp;Due to this geography, naturalized plants and animals deposited by passing ships pre-date Bermuda\u0026rsquo;s settlement (Lefroy 1877; Lefroy 1879; Collett 1987; Sterrer et al. 2004; Marshall et al. 2005).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eUntil 1942 the portions of Bermuda not cleared for buildings or agriculture were densely covered in endemic Bermuda cedar \u003cem\u003eJuniperus bermudiana\u003c/em\u003e forest (Harshberger 1905; Beard 1940; Challinor and Wingate 1971). Weeds inhabited roadsides, fields, and waste ground, comprising mainly accidentally introduced herbs and grasses from Europe and North America (Reade 1883; Lefroy 1884; Britton 1918). Several ornamental species had escaped cultivation, but only a few had established in the understory of the cedar forest (Harshberger 1905; Britton 1918; Beard 1940). Today, however, Bermuda\u0026rsquo;s fragmented woodlands often comprise a canopy of invasive broadleaved trees over a diverse understory of naturalized shrubs, vines, herbs and grasses (Sterrer et al. 2004; Marshall et al. 2005; Wolsak et al. 2018.)\u003c/p\u003e\n\u003cp\u003eA single catastrophic event initiated the shift to woodlands dominated by introduced plants. Between 1944 and 1955 two accidentally introduced insects attacked the Bermuda cedar, killing 90% of the trees in the country within eleven years (Groves 1955). This event, known locally as the Cedar Blight, resulted in the complete loss of tree cover, devastation of local habitats, exposed homes and farmlands to wind and sea spray, and denuded the landscape as tourism was becoming a mainstay of the Bermudian economy (Groves 1955; Challinor and Wingate 1971; Sterrer et al. 2004). To replace the lost vegetation, a national reforestation programme began in 1949 (Groves 1955). Salt-tolerant, fast growing trees and shrubs were imported to provide crucial windbreaks (Challinor and Wingate 1971; Sterrer et al. 2004) and ornamental species from all over the world were imported to beautify the landscape (Whitney 1955; Groves 1955; Challinor and Wingate 1971; Sterrer et al. 2004).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe consequence of the Cedar Blight was extreme ecosystem disturbance resulting in an unforested landscape primed for invasion. The rapid importation of a large volume of plant material, release of these plants directly onto the landscape and selection of plants with characteristics suited to the environmental conditions set the stage for nation-wide plant invasions. The appearance of the country, along with the species composition of its plant communities changed completely in the half-century following the reforestation programme (Sterrer et al 2004; Wolsak et al 2018).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eToday invasive species management and the prevention of new invasions are Government priorities, as highlighted by the recent passage of the Invasive Alien Species Act 2021 (Government of Bermuda 2021). Better tools are needed to improve on-island invasive species management, and to more effectively assess invasion risk from incoming plants by identifying taxa, regions and pathways most likely to contribute new invasive species. An inventory of plants already present in Bermuda and an updated list of invasive and naturalized species is needed to facilitate better management. Bermuda\u0026rsquo;s biodiversity has been well inventoried (Sterrer et al. 2004), but the information is not well reported or accessible.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn this study we compiled a comprehensive checklist of plant species reported from the Bermudian literature and other sources. Using this inventory, we then aimed to: i) update the taxonomy and examine which families and genera are most represented in the introduced flora, ii) categorise the stage in the invasion process reached by each species based on barriers overcome (Richardson et al. 2000; Blackburn et al. 2011), iii) examine the life cycles and life forms of the total introduced flora and those which have escaped cultivation, iv) explore the introduction pathways and whether introductions were intentional, and v) report the native origins of the introduced flora and Bermuda\u0026rsquo;s invasive plants.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e\u003cu\u003eStudy area\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eBermuda is an oceanic archipelago in the north-western Atlantic Ocean, located at 32.4\u0026deg; N and 064.8\u0026deg; W, and 1,052 km east-southeast of Cape Hatteras, North Carolina; the closest point of continental land. The warming influence of the Gulf Stream gives the islands a frost-free, subtropical climate, despite their temperate latitude. The islands form a J-shaped archipelago of 53.7 km\u003csup\u003e2\u003c/sup\u003e, with a maximum elevation of 78 m above sea level. Eight main islands are connected by bridges and a causeway, allowing free movement of people, plants, and animals along the length of the archipelago. \u0026nbsp;An additional 193 islands and rocky islets are scattered in the bays and harbours, 56 of which are inhabited or were at one time (Copeland and Shailer 2011).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eBermuda\u0026rsquo;s resident population of 63,779 (Department of Statistics 2018), gives it a population density of 1,188 per km\u003csup\u003e2\u0026nbsp;\u003c/sup\u003e- one of the highest in the world. Additionally, 808,242 tourists visited Bermuda in 2019 (Bermuda Tourism Authority 2020). This density puts considerable pressure on undeveloped land, natural resources and biodiversity.\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eCompilation of plant names\u0026nbsp;\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eNathaniel Britton\u0026rsquo;s \u003cem\u003eFlora of Bermuda\u003c/em\u003e (1918) is considered the most comprehensive examination of Bermuda\u0026rsquo;s plants and forms the basis of our dataset. We gathered\u0026nbsp;1304 plant names from this text. Other comprehensive 19\u003csup\u003eth\u003c/sup\u003e century publications were consulted to augment Britton\u0026rsquo;s list, primarily the \u003cem\u003eBotany of the Voyage of the Challenger Expeditions\u003c/em\u003e (Hemsley 1884\u003cem\u003e), Plants of the Bermudas, or Somer\u0026apos;s Islands\u003c/em\u003e (Reade 1883), and the \u003cem\u003eBotany of Bermuda\u003c/em\u003e (Lefroy 1884). Other historic texts were consulted (Tables S3\u0026amp;4), but many directly copied from these four lists and added little information.\u003c/p\u003e\n\u003cp\u003eAfter the mid-20\u003csup\u003eth\u003c/sup\u003e century, the literature becomes more focused on ornamental plants rather than the whole flora. Of particular note are the books published by the Garden Club of Bermuda (Whitney 1955; Wardman 1971; Ogden 2002). Unpublished checklists were available for some taxonomic groups. These were usually compiled by amateur enthusiasts or for specific projects, with the palm list of Ogden (2015) being the most comprehensive. Names of native plants were gathered from Britton\u0026rsquo;s list (Britton 1918). A list of species considered invasive was compiled from GRIIS (Copeland et al. 2020) and ten other publications (Table S3).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe herbarium of the Bermuda Natural History Museum at the Bermuda Aquarium, Museum and Zoo (BAMZ) was consulted between August 2020 and January 2023. Plant species considered introduced to Bermuda are separated from indigenous species in this collection. The introduced plants collection and the grass collection were examined and photographed in December 2022.\u003c/p\u003e\n\u003cp\u003eTwo of the largest garden centres on the island were visited in December 2022 to assess the species that are presently available for sale to the public as seeds, seedlings or established plants. The garden centres contributed twenty-nine plant names that are not found in the literature or any other sources. Some of these new taxa are artificial hybrids.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eDuring list compilation, Plants of the World Online (POWO 2023) was used to align 19\u003csup\u003eth\u003c/sup\u003e century taxonomy with currently accepted names for families, genera and species. Older names found to be synonyms of other names in our list were combined into one record. All synonyms and alternate spellings, including misspellings found in the Bermudian literature were retained to allow searching and to maintain connections with the original record. Once the final list of plant species had been compiled, the names were standardized in R using the rWCVP package (Brown et al. 2023; R Core Team 2023), which added accepted binomial, family and author fields to the dataset, according to the World Checklist of Vascular Plants (Govaerts 2023).\u003c/p\u003e\n\u003cp\u003eTwo names are not recognised as synonyms by POWO, and we could not determine from other sources which accepted names they refer to; therefore, these were removed from the list before it was used for analysis. Thirty-one names given by earlier authors that Britton (1918) has treated as erroneous, doubtful or a misidentification were also removed. Thirty-six names found in the historic literature were removed because the author states that the plant did not establish, and it is not recorded in recent sources or known from the island now. Some additional names are valid but do not fit the project aims \u0026ndash; for example six seagrasses were removed so the dataset represents terrestrial flowering plants, ferns and fern allies. Non-vascular plants were excluded.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eIntroduction status classification\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eAll plants were assigned to one of seven introduction classes based on their indigenous or introduced status (Table 1; Tables S3 and S4). Indigenous species were placed into one of two classes, with those only found in Bermuda classed as \u0026lsquo;endemic\u0026rsquo; and those with wider distribution termed \u0026lsquo;native\u0026rsquo;. Introduced species were classified on\u0026nbsp;their success in escaping cultivation and overcoming barriers to survival, reproduction and dispersal.\u0026nbsp;A classification framework (Methods S1) was created based on the concept that species must overcome barriers to move through the stages of invasion (Richardson et al. 2000; Blackburn et al. 2011). We did not consider impact when placing species into the invasive category, as impact is difficult to prove in an unstudied ecosystem like Bermuda\u0026rsquo;s plant communities. Instead, following the frameworks of Richardson et al. (2000) and Blackburn et al. (2011), we used dispersal away from human habitation, and occurrence in multiple habitats to characterise invasive species, as these can be observed with certainty. Our results should, therefore, be comparable to other studies that use these frameworks to define invasive species. Classifications were based on literature and 15 years of plant observations by the first author while employed by the Bermuda Department of Environment and Natural Resources. Any species which could not be classified due to conflicting accounts of its indigenous or introduced status were classified as cryptogenic species of undetermined origin. The resulting seven status classes were: cryptogenic, endemic, native, introduced, casual, naturalized, and invasive.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eLife cycle and life form\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eWe obtained life form data from the Global Inventory of Floras and Traits (GIFT: Weigelt et al. 2020), using the trait 1.2.2 \u0026lsquo;Growth Form\u0026rsquo;, for 1432 Bermudian species and the trait 2.1.1 \u0026lsquo;Lifecycle\u0026rsquo;, for 1455 Bermudian species. We identified the modal life form and life cycle category for each species and used this single category thereafter. We also downloaded life form and life cycle descriptions from the World Checklist of Vascular Plants (WCVP:\u0026nbsp;Govaerts 2023)\u0026nbsp;for 1462 species. Consensus life form and life cycle were then determined by cross referencing GIFT and WCVP data. For 506 species there was good agreement between GIFT and WCVP resulting in a consensus life form based on both sources. Life forms for an additional 642 species appeared just in GIFT, and 213 were determined just from WCVP. For species that did not appear in either trait database, we determined their life form from Britton (1918) or various websites (Tables S3 and S4). For 72 species no information was available, so a life form was assigned from field observations or following an internet image search.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFor 137 species the life form was assigned based on the family. All epiphytic and ground dwelling species in the family Bromeliaceae were assigned the life form \u0026lsquo;bromeliad\u0026rsquo;. The life form \u0026lsquo;graminoid\u0026rsquo; was given to grasses, sedges and rushes in the families Typhaceae, Poaceae, Cyperaceae and Juncaceae. \u0026nbsp;All species in Arecaceae were given the life form \u0026lsquo;palm\u0026rsquo;. The life form \u0026lsquo;fern\u0026rsquo; was assigned to ferns and fern allies in the families Aspleniaceae, Pteridaceae, Polypodiaceae, Osmundaceae, Dennstaedtiaceae and Psilotaceae. \u0026nbsp;The life form \u0026lsquo;cycad\u0026rsquo; was assigned to all members of Cycadaceae and Zamiaceae. The eleven possible categories for consensus life form were: aquatic, bromeliad, cycad, fern, forb/herb, graminoid, palm, shrub, succulent, tree, and vine/climber.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eA consensus life cycle for 480 species was determined from agreement between GIFT and WCVP. Life cycle for an additional 919 species were determined just from GIFT, and 71 were determined just from WCVP, while those that did not appear in either database were determine from Britton (1918) or various websites (Tables S3 and S4). For 86 species no information was available, so a life cycle remained undetermined. The six possible data values for life cycle are: annual, annual or biennial, biennial, biennial or perennial, annual or perennial and perennial. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eDates and pathways of introduction\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eAll casual, naturalized, or invasive species were assigned to an introduction pathway category and subcategory from the Convention on Biological Diversity\u0026rsquo;s categorization of pathways for the introduction of invasive species (CBD 2014; Table S5). Pathways were mostly determined from the literature, otherwise the most likely scenario was assigned based on previous observations and communication with Bermudian habitat managers.\u0026nbsp;We added a category with value 0 named \u0026lsquo;unknown\u0026rsquo; if the pathway could not be determined from the literature, communication with experts or our observations. All non-escaped introduced species were assigned the value \u0026lsquo;cultivated\u0026rsquo; for pathway (Fig. 4b), and given an appropriate sub pathway (Fig.4c). Following categorization of the pathway, each species was also assigned one of six categories under the variable called \u0026lsquo;intentional\u0026rsquo;: accidental, probably accidental, intentional, probably intentional, unaided, or unknown (Table S5).\u003c/p\u003e\n\u003cp\u003eFor early intentional introductions, we were often able to find an introduction year, but for recent introductions this information is often not reported (Tables S3 \u0026amp; S5). For accidental introductions, we could report the year of earliest mention in the literature. In total introduction dates are reported for 285 species and inferred from first mentions in literature or first appearance in herbaria for 1142 species.\u0026nbsp;Species accumulation counts (Fig. 4) assume that following first record the species continues to persist in Bermuda and is therefore added to the cumulative number over time. This of course is not always true, as species are introduced multiple times and some fail to survive one or all introduction attempts.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eGeographic origin\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eWe obtained the geographic origins of Bermuda\u0026rsquo;s plants using the World Checklist of Vascular Plants (WCVP: Govaerts 2023), accessed through the R package \u0026apos;rWCVP\u0026apos; (Brown et al. 2023). Species origins at the scale of botanical continents (corresponding to Taxonomic Database Working Group\u0026mdash;TDWG Level 1, Brummitt 2001), were extracted (August 2023). We re-coded the data so that \u0026lsquo;1\u0026rsquo; represents the native range and \u0026lsquo;0\u0026rsquo; the introduced range (Tables S3 and S4).\u0026nbsp;\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cu\u003eThe total Bermudian flora\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eThe inventory of Bermuda\u0026rsquo;s flora contains 1883 plant names. We removed 296 names from the dataset used for analysis, including 250 taxa with doubtful presence on the island. This left 1587 species which reflects the current state of the Bermudian flora. These 1587 plant species represent 162 plant families. The most species-rich families are Asteraceae (108 species), Fabaceae (100), Poaceae (90), Arecaceae (70) and Lamiaceae (55) (Fig. 1). The 1587 species come from 886 genera, with 570 genera represented by only one species. The most common genus is \u003cem\u003eEuphorbia\u003c/em\u003e with 23 species, followed by \u003cem\u003eFicus\u003c/em\u003e (15 spp.), \u003cem\u003eAgave\u003c/em\u003e (12 spp.) and\u003cem\u003e\u0026nbsp;Ipomoea\u003c/em\u003e (12 spp.).\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eIntroduction status\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eOf Bermuda\u0026rsquo;s 1587 plant species, 1424 (89.7%) are introduced non-natives, while 151 (9.5%) are indigenous and 12 (0.8%) are cryptogenic species of unknown origin (Table 1). Species were classified as cryptogenic when conflicting records of its introduced or indigenous status were found in the literature, with no consensus between authors (Table S3). The indigenous flora is composed of 11 species which are considered island endemics, and 140 native species shared with North and South America and the Caribbean (Table S4).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe majority (77.6%) of the 1424 plants introduced to Bermuda have not escaped cultivation, and remain present only in gardens, farmlands and landscaped situations. These 1104 species were classified as \u0026lsquo;introduced\u0026rsquo; (Table S3). Additionally, 107 species are considered casual, because they have escaped cultivation but do not reproduce sufficiently to maintain wild populations. There are 170 species which have naturalized in Bermuda to form self-sustaining populations outside of cultivation. A further 43 species were classified as invasive representing 3% of the introduced plants and 2.7% of Bermuda\u0026rsquo;s total flora. These invasive species are introduced non-natives which have escaped cultivation and have formed self-sustaining and actively spreading populations (Methods S1; Table S3). They have overcome all barriers to reproduction, recruitment and dispersal (Richardson et al. 2000; Blackburn et al. 2011) and are found at multiple sites in several habitats (Sterrer et al. 2004; Marshall et al. 2005; Wolsak et al. 2018).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eOf the 1424 plants introduced to Bermuda,\u0026nbsp;320 species (22.5% of the introduced flora) have escaped cultivation and are considered casual, naturalized, or invasive. These will be referred to collectively as the \u0026lsquo;escaped species\u0026rsquo;.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1 Species counts in each introduction class and component percentages of the Bermudian flora\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 29.5139%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eIntroduction Status\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12.3264%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSpecies count\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.9236%;\"\u003e\n \u003cp\u003e\u003cstrong\u003e% of total Bermuda flora\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.6181%;\"\u003e\n \u003cp\u003e\u003cstrong\u003e% of indigenous flora\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.6181%;\"\u003e\n \u003cp\u003e\u003cstrong\u003e% of introduced flora\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 29.5139%;\"\u003e\n \u003cp\u003eEndemic\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12.3264%;\"\u003e\n \u003cp\u003e11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.9236%;\"\u003e\n \u003cp\u003e0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.6181%;\"\u003e\n \u003cp\u003e7.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.6181%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 29.5139%;\"\u003e\n \u003cp\u003eNative\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12.3264%;\"\u003e\n \u003cp\u003e140\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.9236%;\"\u003e\n \u003cp\u003e8.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.6181%;\"\u003e\n \u003cp\u003e92.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.6181%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 29.5139%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTotal Indigenous Species\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12.3264%;\"\u003e\n \u003cp\u003e\u003cstrong\u003e151\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.9236%;\"\u003e\n \u003cp\u003e\u003cstrong\u003e9.5\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.6181%;\"\u003e\n \u003cp\u003e100\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.6181%;\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 29.5139%;\"\u003e\n \u003cp\u003eIntroduced (not escaped)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12.3264%;\"\u003e\n \u003cp\u003e1104\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.9236%;\"\u003e\n \u003cp\u003e69.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.6181%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.6181%;\"\u003e\n \u003cp\u003e77.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 29.5139%;\"\u003e\n \u003cp\u003eCasual\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12.3264%;\"\u003e\n \u003cp\u003e107\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.9236%;\"\u003e\n \u003cp\u003e6.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.6181%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.6181%;\"\u003e\n \u003cp\u003e7.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 29.5139%;\"\u003e\n \u003cp\u003eNaturalized\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12.3264%;\"\u003e\n \u003cp\u003e170\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.9236%;\"\u003e\n \u003cp\u003e10.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.6181%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.6181%;\"\u003e\n \u003cp\u003e11.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 29.5139%;\"\u003e\n \u003cp\u003eInvasive\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12.3264%;\"\u003e\n \u003cp\u003e43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.9236%;\"\u003e\n \u003cp\u003e2.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.6181%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.6181%;\"\u003e\n \u003cp\u003e3.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 29.5139%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTotal Introduced Species\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12.3264%;\"\u003e\n \u003cp\u003e\u003cstrong\u003e1424\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.9236%;\"\u003e\n \u003cp\u003e\u003cstrong\u003e89.7\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.6181%;\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.6181%;\"\u003e\n \u003cp\u003e100\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 29.5139%;\"\u003e\n \u003cp\u003eCryptogenic\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12.3264%;\"\u003e\n \u003cp\u003e12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.9236%;\"\u003e\n \u003cp\u003e0.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.6181%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.6181%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 29.5139%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTotal Bermuda flora\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12.3264%;\"\u003e\n \u003cp\u003e\u003cstrong\u003e1587\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.9236%;\"\u003e\n \u003cp\u003e\u003cstrong\u003e100\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.6181%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.6181%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eIntroduced families and genera\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eThe introduced flora of Bermuda contains 1424 species from 152 families, with 34 families represented by a single species (Table S2). The most common introduced families are Asteraceae (98 spp.), Fabaceae (95 spp.), Poaceae (69 spp.), Arecaceae (69 spp.) and Lamiaceae (54 spp.) (Fig.1).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe 107 casual species come from 48 plant families, with the Poaceae (13 spp.), Asteraceae (8 spp.), Lamiaceae (7 spp.) and Brassicaceae (6 spp.) most represented. The 170 naturalized species come from 61 plant families; of which 29 are represented in the naturalized flora by only one species (Table S2). The families with the most naturalized species are Poaceae (20 spp.), Asteraceae (15 spp.), Fabaceae (9 spp.), and Plantaginaceae (8 spp.).\u003c/p\u003e\n\u003cp\u003eThe 43 species classified as invasive come from 30 families, with 20 families represented by a single invasive species. The most represented families in Bermuda\u0026rsquo;s invasive flora are Ranunculaceae, Asparagaceae and Myrtaceae each with three invasive species (Table S2). Among Bermuda\u0026rsquo;s invasive families Petiveriaceae stands out as it does not contain any indigenous species, and the two introduced species from this family, \u003cem\u003eRivina humilis\u003c/em\u003e and \u003cem\u003eTrichostigma octandrum\u003c/em\u003e, are both invasive.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe 320 species that have escaped captivity to become casual, naturalized, or invasive, all together represent 229 genera from 82 families. The most frequently escaped families are Poaceae (34 spp.), Asteraceae (25spp.) and Fabaceae and Lamiaceae with 12 species each. The genus with the most escaped plants is \u003cem\u003eEuphorbia\u003c/em\u003e with 7 species, followed by \u003cem\u003eOxalis\u003c/em\u003e (5 spp.) and \u003cem\u003eErigeron, Ipomoea\u003c/em\u003e and \u003cem\u003eRanunculus\u003c/em\u003e with 4 species each.\u0026nbsp;The 43 invasive species represent 35 genera, with three species of \u003cem\u003eAsparagus\u003c/em\u003e and \u003cem\u003eClematis\u003c/em\u003e, and two species of \u003cem\u003eAbutilon\u003c/em\u003e, \u003cem\u003eCardiospermum, Heptapleurum\u003c/em\u003e and \u003cem\u003ePittosporum\u003c/em\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe 1104 introduced species belong to 139 plant families. The most represented families among these cultivated species are Fabaceae (83 spp.), Asteraceae (73 spp.), Arecaceae (63 spp.), Lamiaceae (42 spp.) and Solanaceae (37 spp.). The 1104 introduced but not escaped species come from 662 genera, with 450 genera having a single introduced species. \u0026nbsp;The most represented is \u003cem\u003eFicus\u003c/em\u003e with 14 species, followed by \u003cem\u003eEuphorbia\u003c/em\u003e (11 spp.), \u003cem\u003eAgave\u003c/em\u003e (10 spp.), \u003cem\u003eBegonia, Senna\u003c/em\u003e and \u003cem\u003eSolanum\u003c/em\u003e (9 spp. each), and\u003cem\u003e\u0026nbsp;Salvia\u003c/em\u003e (8 spp.). \u0026nbsp;Comparison of the escaped flora with those remaining only in cultivation shows that Asphodelaceae, Zingiberaceae and Annonaceae are the families with the most species introduced to Bermuda but failing to naturalize, with 11, 10 and 8 species respectively. The genera that are most widely introduced but have not escaped include \u003cem\u003eSenna\u003c/em\u003e and \u003cem\u003eSolanum\u003c/em\u003e with 9 introduced species each, and \u003cem\u003eClerodendrum\u003c/em\u003e, \u003cem\u003eErythrina\u003c/em\u003e and \u003cem\u003eHibiscus\u0026nbsp;\u003c/em\u003ewith 7 species each.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eLife forms\u0026nbsp;\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eMost of the 1424 plants introduced to Bermuda are herbs/forbs (40%) followed by trees (18%), shrubs (17%), vines/climbers (7%), graminoids (5%), succulents (5%) and palms (5%). Non-woody life forms make up the majority of the escaped flora which is 54% forbs and 12% graminoids (Fig. 2). Forbs comprise 61% of both casual and naturalized species, followed by graminoids (12% of casual species and 14% of naturalized species). In contrast, woody life forms make up much of the invasive flora with 33% being trees and 23% shrubs followed by 6% vines/climbers. Bermuda\u0026rsquo;s 43 invasive plants display seven life forms, including 4 forbs, 4 ferns, one grass, 9 vines, one palm, 10 shrubs and 14 trees (Fig. 2; Table S3).\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eLife cycles\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003ePerennial life cycles dominate the introduced flora, with 1112 perennial species (78%). Among the 320 escaped species, 25% are annuals and 55% are perennials. The remainder are some combination of annual, biennial or perennial as multiple types of life cycle were reported in the sources consulted (Table S3). Perennial life cycles are most dominant among the invasive species also, with only two definite annuals (\u003cem\u003eAbutilon\u0026nbsp;theophrasti\u003c/em\u003e and \u003cem\u003eCardiospermum\u0026nbsp;halicacabum\u003c/em\u003e) and \u003cem\u003eCardiospermum\u0026nbsp;grandiflorum\u003c/em\u003e classed as \u0026lsquo;annual or perennial\u0026rsquo;. The remaining 40 invasive species (93%) were perennial.\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eNative range of the introduced flora\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eBermuda\u0026rsquo;s introduced flora contains plants from all nine continents in the Taxonomic Database Working Group (TDWG) continental scheme (Brummitt 2001; Govaerts 2023). Some species were native to five or six TDWG continents, making comparative percentages uninformative. The major sources of introduced species are Temperate Asia (352 spp.), Southern America (336 spp.), Northern America (322 spp.), Tropical Asia (282 spp.) and Africa (278 spp.). The 320 plants that have escaped cultivation also originate from all nine continents (Fig. 3; Table S3), with Temperate Asia (117 spp.), Africa (99 spp.) and Northern America (90 spp.) as the major sources. The 43 invasive species are native to eight continents, excluding Antarctica. Again, Temperate Asia is the most represented potential source, supplying 18 invasive species, followed by Tropical Asia and Africa (12 spp. each), Southern America (10 spp.) and Australasia (7 spp.) (Fig. 3; Table S3).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eWe grouped the nine TDWG botanical continents into broader areas that species were native to, giving five combinations of continental origins (Table 2). We examined the conversion rate of total species in all introduced classes to invasive species. Oceania (includes Australasia, Antarctica, and Pacific) had the highest conversion rate (8.2%) despite the fewest introductions originating from this part of the world. \u0026nbsp;Asia (Temperate Asia and Tropical Asia) and Africa had rates roughly half as high, with 4.7% and 4.3% respectively. The Americas (Northern and Southern America) had a low conversion rate despite a large number of introductions from this region (Table 2). European species had the lowest conversion rate with only 1% of introductions becoming invasive.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2 Conversion rates of introduced species into invasive species by grouped continents of origin\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 24.4851%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eNative Origin\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 24.9428%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eInvasive in Bermuda\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 28.3753%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAll Introduced to Bermuda\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 22.1968%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eConversion Rate (%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 24.4851%;\"\u003e\n \u003cp\u003eOceania\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 24.9428%;\"\u003e\n \u003cp\u003e12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 28.3753%;\"\u003e\n \u003cp\u003e147\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 22.1968%;\"\u003e\n \u003cp\u003e8.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 24.4851%;\"\u003e\n \u003cp\u003eAsia\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 24.9428%;\"\u003e\n \u003cp\u003e30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 28.3753%;\"\u003e\n \u003cp\u003e636\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 22.1968%;\"\u003e\n \u003cp\u003e4.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 24.4851%;\"\u003e\n \u003cp\u003eAfrica\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 24.9428%;\"\u003e\n \u003cp\u003e12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 28.3753%;\"\u003e\n \u003cp\u003e279\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 22.1968%;\"\u003e\n \u003cp\u003e4.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 24.4851%;\"\u003e\n \u003cp\u003eAmericas\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 24.9428%;\"\u003e\n \u003cp\u003e16\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 28.3753%;\"\u003e\n \u003cp\u003e658\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 22.1968%;\"\u003e\n \u003cp\u003e2.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 24.4851%;\"\u003e\n \u003cp\u003eEurope\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 24.9428%;\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 28.3753%;\"\u003e\n \u003cp\u003e199\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 22.1968%;\"\u003e\n \u003cp\u003e1.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cu\u003e\u0026nbsp;\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003e\u003cu\u003e\u0026nbsp;\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003e\u003cu\u003e\u0026nbsp;\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eIntroduction pathways of casual, naturalized and invasive flora\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eThe majority of Bermuda\u0026rsquo;s 1424 introduced plants were brought to the island intentionally (88%), while 11% were accidental introductions, and for 1% the introduction type could not be determined from the literature. For the 320 species in the escaped flora, 53% were intentional introductions, while 46% were accidental and 1% were unknown (Table S5). Among invasive species, 93% were intentionally introduced, while 7% were accidentally introduced.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe majority of casual and naturalized plants arrived as contaminants in imported goods prior to 1918. These historic contaminated imports account for 45% of casual species and 42% of naturalized species introductions (Table S5).\u0026nbsp;The introduction of plants as contaminants is probably under-represented by these figures, as the true number of plants that arrived but did not establish, or were not reported, cannot be known.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eEscape from cultivation of plants imported for ornamental purposes accounted for 28% of casual species and 29% of naturalized species. Plants imported for agriculture, particularly fodder grasses, account for 10% of naturalized species introductions.\u003c/p\u003e\n\u003cp\u003eOf Bermuda\u0026rsquo;s 43 invasive species, 36 species (84%) have escaped from cultivation, with three introduced as fruit trees, and 33 species (77% of the invasive flora) for ornamental purposes. The three trees with edible fruits are the Surinam cherry \u003cem\u003eEugenia uniflora\u003c/em\u003e, loquat\u003cem\u003e\u0026nbsp;Eriobotrya japonica\u0026nbsp;\u003c/em\u003eand guava \u003cem\u003ePsidium guajava\u003c/em\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAnother four invasive species were intentionally released into coastal habitats for erosion control or as windbreaks, namely the Australian whistling pine \u003cem\u003eCasuarina equisetifolia\u003c/em\u003e, Madagascar olive \u003cem\u003eNoronhia emarginata\u003c/em\u003e, beach naupaka \u003cem\u003eScaevola taccada\u003c/em\u003e and seaside creeping daisy \u003cem\u003eSphagneticola trilobata.\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eIntroduction date or earliest record\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eThe majority of Bermuda\u0026rsquo;s introduced plants arrived between about 1830 and 1930 (Fig. 4). The sharpest increase in the introduction of species that were released from, or escaped cultivation occurred between about 1880 and 1918 (Fig.4b). Of Bermuda\u0026rsquo;s 43 invasive species, 26 were already present when Dr Britton surveyed Bermuda\u0026rsquo;s flora between 1905 and 1912 (Britton 1918; Table S3). From the mid-20\u003csup\u003eth\u003c/sup\u003e century onward the rate of introduction of escaped species flattens off, while total introductions continue to increase (Fig. 4a and 4b). New pathways of introduction appear in the late 20\u003csup\u003eth\u003c/sup\u003e century, with the first record of a casual species attributed to transport on the wheels of an airplane appearing as a herbarium specimen in 1981 (Fig 4b).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe introduction of two naturalized plants predate settlement, having been recorded on the islands in 1593 (Fig. 4a; Lefroy 1884; Collett 1987; Sterrer et al. 2004). Once the British arrived in Bermuda in 1609 a low volume of plant introductions began, with little increase for 200 years (Fig.4a). Bermuda\u0026rsquo;s colonial governor from 1871 to 1877, Sir John Henry Lefroy was a keen botanist who exchanged plants with botanical gardens in the United States, and Europe (Lefroy 1884; Wolsak et al. 2018) and was responsible for introducing more species to Bermuda than any other person (Marshall et al. 2005). The activities of Governor Lefroy resulted in a cluster of well-documented introductions in the 1870\u0026rsquo;s (Fig.4a; Reade 1883; Lefroy 1884; Britton 1918). Other large increases in first mentions of introduced plant species result from the publication of major botanical works in 1883, 1884, 1918, 1933 and 1971 (Reade 1883; Hemsley 1884; Lefroy 1884; Britton 1918; Baker 1933 in Jones 1986; Wardman 1971).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe 1587 indigenous and introduced plants reported in our inventory represent Bermuda\u0026rsquo;s first checklist of accepted plant names with modern taxonomy and a standardized classification of their introduction status, life form, native range and date of first record. Our analysis of the inventory indicates that within the Bermudian flora introduced species outnumber indigenous species 9:1, and escaped introductions outnumber indigenous plants 2:1 (Table 1). The introduced Bermudian flora comprises 1424 species, 320 (22.5%) of which are found outside of cultivation, including 43 (3%) that have become invasive. Here, we discuss these findings in the context of Bermuda\u0026rsquo;s economic development stages, present and historic landscapes, and we compare Bermuda to patterns in naturalized floras globally and on other islands.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eEconomic development stages and plant introductions\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eBermuda has passed through various stages in its socioeconomic development since the islands were permanently settled. Plants were imported at each stage through varying trade and transport links to meet various goals (Collett 1987; Sterrer et al. 2004), which influenced both introduction pathways and propagule pressure, and in turn dictated the potential for invasion (Essl et al. 2019).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe British settled Bermuda in 1609 and a permanent colony was established in 1612 (Lefroy 1877). The earliest introductions were crops and medicinal plants critical to survival of the new colony, which were sent from Europe and are well reported in the colonial records (Lefroy 1877; Lefroy 1879; Collett 1987).\u0026nbsp;Two naturalized species, papaya \u003cem\u003eCarica papaya\u003c/em\u003e and the European olive \u003cem\u003eOlea europaea\u003c/em\u003e have the earliest recorded mentions in the literature from 1593 (Fig. 4a), giving a current residence time of 430 years (Collett 1987; Sterrer et al. 2004). Lefroy (1884) reports that \u003cem\u003eOlea europaea\u003c/em\u003e was already \u0026ldquo;naturalized, probably from seeds sown by the crews of Spanish vessels visiting the islands or wrecked on them in the sixteenth century\u0026rdquo; when the first colonists arrived in 1609. The next oldest naturalized species is the common fennel \u003cem\u003eFoeniculum vulgare\u003c/em\u003e introduced in 1616 as seeds sent from Europe (Lefroy 1884; Collett 1987). Today fennel is naturalized on grassy hillsides and among sand dunes along the South Shore.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe earliest reported non-edible introductions are, the wild indigo \u003cem\u003eIndigofera suffruticosa\u003c/em\u003e and castor oil plant \u003cem\u003eRicinus communis\u003c/em\u003e both introduced prior to 1623, and cotton \u003cem\u003eGossypium herbaceum\u003c/em\u003e introduced in 1624, all of which were imported as cash crops for export (Lefroy 1884; Hemsley 1884; Collett 1987). European colonies in the New World sought to develop all potential commercial ventures, so plants arriving at this time were intended to generate profits. Many new plants were being discovered by European explorers in the mid-17\u003csup\u003eth\u003c/sup\u003e century and these were sent to the colonies for trial as commercial enterprises (Lefroy 1879; Lefroy 1884; Collett 1987; Sterrer et al. 2004).\u003c/p\u003e\n\u003cp\u003eThe earliest mention of a non-agricultural plant is the pasture weed \u003cem\u003eSida acuta\u003c/em\u003e. On November 10\u003csup\u003eth\u003c/sup\u003e, 1669 the Governor Sir John Heydon issued a notice to all tenants that they are to pull up the wireweed or risk forfeiting their land for neglect of it (Lefroy 1879). Governor Lefroy has made a footnote on this record, reporting \u003cem\u003eSida acuta\u003c/em\u003e was \u0026ldquo;still a great pest\u0026rdquo; over 200 years later (Lefroy 1879). From the early years of the Bermuda colony up until the 1930\u0026rsquo;s hay was imported from North America to feed the island\u0026rsquo;s horses (Lefroy 1884; Sterrer et al 2004) providing an important pathway for weeds to enter as contaminants (Fig. 4b and 4c). It is likely several naturalized plants entered the island this way, both native North American species, and those European weeds with naturalized populations in eastern North America.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eBermuda had primarily a trade economy from the 17th to 19\u003csup\u003eth\u003c/sup\u003e century, during which Bermudian seafarers travelled widely and brought home many plants they encountered abroad, which were planted in a \u0026lsquo;trial and error\u0026rsquo; fashion (Reade 1883; Lefroy 1884); a practice which continued into the 20\u003csup\u003eth\u003c/sup\u003e century (Britton 1918; Jones 1986). Governor Lefroy laments at length that ornamental horticulture, particularly flower gardening, was not widely undertaken by Bermudians in the 1870\u0026rsquo;s, a situation he began to remedy with the import of seeds and plants from all over the world and professional gardeners from Britain (Lefroy 1884).\u003c/p\u003e\n\u003cp\u003eAttitudes to ornamental plants did change in this period, with most of Bermuda\u0026rsquo;s total plant species, and ornamentals in particular, introduced between 1830 to 1930 (Fig. 4c). Landscaping of public spaces began in this period (Reade 1883; Britton 1918), including the establishment of the Public Gardens in 1898, which would become the Bermuda Botanical Gardens in 1958 (Department of Agriculture 1961). As Bermuda transitioned to a service economy based on tourism in the 20\u003csup\u003eth\u003c/sup\u003e century, the interest in ornamental plants grew (Department of Agriculture 1961; Sterrer et al. 2004).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eLegacy of the Cedar Blight\u0026nbsp;\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eIn the years immediately following the Cedar Blight of the 1940s, Bermuda\u0026rsquo;s landscape changed from one covered with relatively few indigenous species to one dominated by a diversity of introduced plants (Groves 1955;\u0026nbsp;Challinor and Wingate 1971;\u0026nbsp;Sterrer et al. 2004; Wolsak et al. 2018). The reforestation programme that began in 1949 has been acknowledged as responsible for the spread of now-invasive plants (Sterrer et al. 2004), however, we found relatively few introduction dates or first mentions of escaped species around 1949 (Fig. 4a). This suggests that although the numbers of plants being imported, propagated and planted at that time may have been high, few new species were being added to the flora. It is likely increased propagule pressure from species already present, combined with the arrival of new seed-dispersing birds and a newly barren landscape, triggered a population expansion for many planted species.\u003c/p\u003e\n\u003cp\u003eThe reforestation programme involved planting imported trees, palms and shrubs along roadsides, on golf courses, on the islands of Hamilton Harbour and on all Government-owned land (Groves 1955; Challinor and Wingate 1971; Sterrer et al. 2004). Early in the programme, plantings suffered considerable losses due to wind and drought, demonstrating the need for hardier plants and the establishment of good windbreaks (Groves 1955). It is likely this focus on selecting woody species suited to Bermuda\u0026rsquo;s harsh environmental conditions that precipitated their current dominance of the invasive flora.\u0026nbsp;Trees and shrubs represent only 35% of the introduced flora, and only 18% of escaped species, but make up 56% of the invasive flora (Fig. 2).\u0026nbsp;The reforestation programme facilitated the release of these salt-tolerant and wind-adapted species directly into the environment on a country-wide scale, which hastened their advancement along the invasion stage continuum. Considerable government funds were spent on these planting schemes (Groves 1955). Ironically, a substantial amount is now spent each year on invasive plant and habitat management and roadside weed control as a legacy of the Cedar Blight.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eComparing Bermuda\u0026rsquo;s flora to other islands\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eOur inventory revealed a high proportion of introduced species (89.7%) in the Bermudian flora compared to just 9.5% indigenous plants. This proportion is higher than reported for other oceanic islands such as the Azores, which host 1002 taxa that are 69% introduced and 31% indigenous (Silva and Smith 2004). Bermuda also has a high proportion of naturalized species compared to indigenous ones. In a comparison of island floras across the globe, Essl et al. (2019) reported that 26% of the islands examined had more naturalized than native species. With 170 naturalized species to 151 natives, Bermuda fits within this minority.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThere are several patterns in Bermuda\u0026rsquo;s naturalized and invasive flora that are consistent with reported global patterns. These include ornamental horticulture as the primary pathway of introduction of invasive species (Gu\u0026eacute;zou et al. 2010, Rejm\u0026aacute;nek 2014; van Kleunen et al. 2018; Rojas-Sandoval and Ackerman 2021), and thus intentional introduction being responsible for the majority of invasive species (Silva and Smith 2004; van Kleunen et al. 2018; Rojas-Sandoval and Ackerman 2021). In addition, species from Asia are well represented in the naturalized flora of Bermuda reflecting strong representation among naturalized species globally (van Kleunen et al. 2015; Py\u0026scaron;ek et al 2017). Worldwide, islands also have more naturalized woody species than annual herbs (Py\u0026scaron;ek et al 2017), a pattern that Bermuda adheres to.\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eComparing families\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eAt the global scale the naturalized flora is dominated by the Fabaceae, Poaceae and Asteraceae families (Py\u0026scaron;ek et al. 2017), a trend that also appears at the regional scale in the West Indies (Rojas-Sandoval and Ackerman 2021) and Central America (Rojas-Sandoval et al. 2023), and among island groups such as the Galapagos (Gu\u0026eacute;zou et al. 2010), and Puerto Rico and the Virgin Islands (Rojas-Sandoval and Acevedo-Rodr\u0026iacute;guez 2015). Bermuda\u0026rsquo;s introduced and naturalized flora is also dominated by Asteraceae, Fabaceae and Poaceae, however these families are not well represented in the invasive flora (Fig.1). Bermuda has only two Asteraceae classified as invasive, one Poaceae and one Fabaceae (Tables S2 \u0026amp; S3). This departure should be subjected to future study. \u0026nbsp;It is likely a result of our strict application of the term \u0026lsquo;invasive\u0026rsquo; only to plants widely dispersed into multiple wild habitats, while others consider agricultural and garden weeds as invasive (e.g.\u0026nbsp;Rojas-Sandoval and Acevedo-Rodr\u0026iacute;guez 2015). For example, we classified \u003cem\u003eCenchrus purpureus\u003c/em\u003e as naturalized but not invasive (Table S3) because although it is dominant on the edge of freshwater marshes where it was historically planted as fodder, it has not dispersed away from these points of introduction into other habitats. \u003cem\u003eCenchrus purpureus\u003c/em\u003e does appear on invasive species lists for other islands such as Cuba\u0026nbsp;(Oviedo Prieto and Gonz\u0026aacute;lez-Oliva 2015), Puerto Rico (Rojas-Sandoval and Acevedo-Rodr\u0026iacute;guez 2015), and the Virgin Islands (Rojas-Sandoval and Acevedo-Rodr\u0026iacute;guez 2015). Similarly, many Asteraceae that appear as agricultural weeds in Bermuda were classified as naturalized since farmland is not extensive, and therefore these plants are not widespread.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe palm family Arecaceae is an important source of potentially invasive plants in tropical regions, with a high risk of spread through bird dispersal of species with fleshy fruits (Rejm\u0026aacute;nek 2014). Palms were the fourth most introduced family in the Bermudian flora (Fig. 1; Table S2), due to the low native palm diversity (one endemic species only) and the popularity of palms in ornamental horticulture, particularly for tourism developments. Thus far Bermuda has only a single invasive palm, the Chinese fan palm \u003cem\u003eLivistona chinensis\u003c/em\u003e, however naturalized populations of \u003cem\u003ePhoenix reclinata\u0026nbsp;\u003c/em\u003eand\u003cem\u003e\u0026nbsp;Ptychosperma elegans\u003c/em\u003e have appeared in natural habitats in recent years which may continue to persist and spread in the future.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eComparing life forms\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eAlthough herbs and forbs form the largest proportion of Bermuda\u0026rsquo;s introduced flora (40% of introduced species), they represent only 9% of the invasive flora (Fig. 2). This is in contrast to the regional pattern within the West Indies where herbs comprise the largest segment 29% (Rojas-Sandoval and Ackerman 2021) to 31% (Rojas-Sandoval et al. 2017) of the invasive flora. As with families, this discrepancy is likely due in part to the way we defined invasive species and life forms. Ruderal and agricultural habitats are important for invasive plants in the West Indies (Rojas-Sandoval et al. 2017). As neither ruderal nor agricultural land is extensive in Bermuda, weeds of these habitats, which are often herbaceous, did not meet the dispersal into multiple habitats criteria in our framework (Methods S1). Also, we used the value \u0026lsquo;ferns\u0026rsquo; as a separate life form, comprising an additional 9% of Bermuda\u0026rsquo;s invasive flora (Fig. 2), while other studies did not separate ferns from other herbaceous life forms (Rojas-Sandoval et al. 2017; Rojas-Sandoval and Ackerman 2021). The poor representation of herbs in Bermuda\u0026rsquo;s invasive flora is also likely a reflection of lower propagule pressure compared to woody life forms.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eComparing pathways\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eA review of invasive species across 18 Caribbean island groups showed that 18% were unintentional introductions, while 82% were intentionally introduced (Rojas-Sandoval and Ackerman 2021). Bermuda\u0026rsquo;s invasive species broadly follow this regional introduction pattern, with 7% accidental and 93% intentional introductions, suggesting that biosecurity measures aimed at intentional imports of plant material and seeds should be prioritized over those to prevent stowaways and contaminants. \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eOrnamental horticulture is a significant pathway of introduction for naturalized and invasive plant species globally (Rejm\u0026aacute;nek 2014; van Kleunen et al. 2018), regionally within the wider Caribbean (Rojas-Sandoval et al. 2017; Rojas-Sandoval and Ackerman 2021) and on other oceanic archipelagos such as the Galapagos (Gu\u0026eacute;zou et al. 2010) and the Azores (Smith and Silva 2004). As 77% of Bermuda\u0026rsquo;s invasive plants also arrived for ornamental purposes, the need for improved regulation of both commercial and private imports of ornamental plants is apparent.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eDeliberately introduced, woody life forms, particularly those producing edible fruit, are overrepresented in the naturalized floras of islands globally (Py\u0026scaron;ek et al. 2017), a pattern which Bermuda follows.\u0026nbsp;The recent covid-19 pandemic has increased awareness of Bermuda\u0026rsquo;s reliance on imports and resulting lack of food security. This has made curbing the commercial sale and private distribution of invasive plants that produce edible products particularly problematic.\u0026nbsp;The availability of seeds from online retailers has widened the pool of what is available to Bermudian home gardeners and the island\u0026rsquo;s commercial horticulture sector. Therefore, the risk of a new invasive plant arriving is probably very high.\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eDonor regions\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eBermuda\u0026rsquo;s native flora contains Caribbean species at the northern limits of their range, overlapping species shared with southeastern North America (Hemsley 1884; Britton 1918; Groves 1955; Sterrer et al. 2004), so it is not surprising to find plants from both tropical and temperate continents naturalizing under these conditions. Asia, particularly temperate Asia, is the largest donor of naturalized plants to other regions of the world (van Kleunen et al. 2015; Py\u0026scaron;ek et al 2017). Accordingly, temperate Asia is the most important donor to Bermuda\u0026rsquo;s flora, supplying the most invasive species (18 spp.), the most escaped species (117 spp.) and the most introduced species (352 spp.). The Southern hemisphere continents are underrepresented as donors of naturalized plants at the global scale (van Kleunen et al. 2015) but this is not the case for Bermuda\u0026rsquo;s invasive flora, where South America, Africa and Australasia are well represented (Fig. 3). \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eLimitations of this study and areas for future research\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eSynthesizing information from historic texts, particularly those not based on direct observation by the authors (eg. Hemsley 1884) introduces a risk of reporting error. Similarly, the use of data from non-scientific sources and unconfirmed reports from non-specialists introduces the risk of mis-identification of species. By removing doubtful names at the start of the analysis, we are confident that we minimized these sources of error as much as possible. Our inventory has identified several introduced and invasive plants that need further expert verification, as we suspect they are still mis-identified. We anticipate that following revision by family or genera experts the names and numbers of invasive and naturalized species in this dataset may change. Bermudian resources for identifying Poaceae in particular are lacking, and given the importance of this family in both the native and naturalized floras (Fig.1), this should be addressed as a priority.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003ePreparation of this inventory did not involve any study-specific field surveys of naturalized or invasive vegetation, so we also anticipate new field data will improve our plant list and future assessment of species invasion stages. Equally importantly, any casual or introduced species that are no longer present can be noted as such, although this is hard to verify, particularly as known casual populations are not monitored. Future work should investigate impacts of invasive plants following field surveys, as we made no attempt to incorporate impact into our classification. Regardless of these limitations our inventory is an important baseline and provides a Bermuda data point and additional oceanic island data point for global studies.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eImproving representation of the introduced flora in national herbarium collections should also be a priority for future work. Of the 273 sheets we examined at the Bermuda Natural History Museum, the indigenous, naturalized and invasive flora were well represented, while only 53 introduced species that remain in cultivation were present. Expanding the collection will facilitate other botanical studies, allow confirmation of species identity by experts and aid future identification of new naturalized populations of represented plants.\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eImplications for risk assessments\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eWhen Bermuda\u0026rsquo;s State of the Environment Report was commission 20 years ago it was noted that \u0026ldquo;not all policy-makers or members of the public share the view that invasive species negatively impact biodiversity\u0026rdquo; (Marshall et al. 2005) and sadly little has changed in this regard. Support for restrictions on plant sales and cooperation with the risk assessment process for imports is low.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eBy quantifying how dominated Bermuda\u0026rsquo;s flora is by introduced species and highlighting that intentional introduction of ornamental plants has resulted in most of Bermuda\u0026rsquo;s problematic invasives, we hope to demonstrate the extent of the problem to the horticulture sector, policy makers and the public. Our inventory will be a resource for those undertaking risk assessments as well as horticulturalists seeking indigenous species or non-naturalized introductions for their planting projects.\u0026nbsp;\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eSevere habitat degradation during the 20\u003csup\u003eth\u003c/sup\u003e century, followed by active reforestation with introduced species has left Bermuda with a substantial invasive plant problem (Sterrer 2004; Marshall et al. 2005; Wolsak et al. 2018; Copeland et al. 2020). By creating this inventory of the Bermudian flora, and developing a standardized invasion stage classification (Methods S1), we have captured the current state of this problem and its origins. Future reapplication of this invasion stage classification will allow new introductions to be tracked and emerging naturalized and invasive species to be identified, which should allow timely mobilization of resources to address them. Additionally, by demonstrating that ornamental horticulture was responsible for the introduction of most invasive plants, we hope to encourage greater cooperation with risk assessments and biosecurity policies.\u0026nbsp;\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors would like to thank the reviewers for their time and helpful comments. AC is supported by a Durham Doctoral Scholarship from the Faculty of Science, Durham University, and wishes to thank the Garden Club of Bermuda for additional support. We also acknowledge the assistance of the Bermuda Government, Department of Environment and Natural Resources.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAC compiled the species list, undertook data analysis and wrote the manuscript. WD advised on data collation, preparation, analysis and presentation, and edited the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u0026nbsp;\u003c/strong\u003eThe authors have no conflicts or competing interests\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSupplemental material\u003c/strong\u003e\u003c/p\u003e\n\u003cul\u003e\n \u003cli\u003eS1. Methods: Classification framework for invasion stage of introduced species.\u003c/li\u003e\n \u003cli\u003eS2. Table of number of species per family across the seven introduction status classes.\u003c/li\u003e\n \u003cli\u003eS3. Table of status, life form, life cycle and native origin for introduced, casual, naturalized, invasive and cryptogenic species.\u003c/li\u003e\n \u003cli\u003eS4. Table of status, life form, life cycle and native origin for endemic and native species.\u003c/li\u003e\n \u003cli\u003eS5. Table of introduction dates and pathways for casual, naturalized and invasive species.\u003c/li\u003e\n\u003c/ul\u003e"},{"header":"References","content":"\u003cp\u003eBeard JS (1940) The Woodlands of Bermuda. Empire Forestry Journal, Vol. 19 No. 2 (December 1940):258-263. \u003ca href=\"https://www.jstor.org/stable/42594799\"\u003ehttps://www.jstor.org/stable/42594799\u003c/a\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eBermuda Tourism Authority (2020) 2019 Visitor Arrivals Report: Full Year. The Business Intelligence \u0026amp; Technology Division of the Bermuda Tourism Authority (BTA), Hamilton, Bermuda.\u0026nbsp;\u003ca href=\"https://www.gotobermuda.com/sites/default/files/202206/2019_bermuda_visitor_arrivals_report_final_compressed.pdf\"\u003ehttps://www.gotobermuda.com/sites/default/files/202206/2019_bermuda_visitor_arrivals_report_final_compressed.pdf\u003c/a\u003e. 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CABI, Wallingford, UK, vi + 384 pp.\u0026nbsp;\u003ca href=\"https://doi.org/10.1079/9781800623453.0000\"\u003ehttps://doi.org/10.1079/9781800623453.0000\u003c/a\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eWolsak S, Wingate D, Cronk Q (2018)\u0026nbsp;Environmental change in the terrestrial vegetation of Bermuda: Revisiting Harshberger (1905). Brittonia, 70: 257-275.\u0026nbsp;\u003ca href=\"https://doi.org/10.1007/s12228-017-9509-x\"\u003ehttps://doi.org/10.1007/s12228-017-9509-x\u003c/a\u003e\u0026nbsp; \u0026nbsp;\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"biological-invasions","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"binv","sideBox":"Learn more about [Biological Invasions](https://www.springer.com/journal/10530)","snPcode":"10530","submissionUrl":"https://submission.nature.com/new-submission/10530/3","title":"Biological Invasions","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"checklist, invasion stage, introduced plants, island flora, alien species","lastPublishedDoi":"10.21203/rs.3.rs-4958039/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4958039/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Abstract\nScreening incoming plants for potentially invasive species is key to preventing new invasions on islands. Doing this effectively requires knowledge of plants already present and invasive in the country, and which pathways, donor regions and families have previously contributed the most invasives. As Bermuda previously lacked such a dataset, we compiled a comprehensive inventory of the native, introduced, casual, naturalized and invasive plants from historic and modern literature, herbarium records and field visits. The inventory contains updated taxonomy, pathways and dates of introduction, native geographic range, life form, and naturalization status for 1587 vascular plants from 162 families. Of these, 1424 species (89.7%) are introduced to Bermuda, while 151 (9.5%) are native. Classifying stage of invasion shows 320 species (22.5% of the introduced flora) have escaped cultivation to form casual, naturalized or invasive populations. Bermuda currently has 43 invasive plants, representing 2.7% of the total flora and 3% of the introduced flora. Among the invasive species 25 (56%) are trees and shrubs, mostly of Asian origin. Ornamental horticulture was the introduction pathway for 77% of invasive plants, emphasizing the need for further collaboration with the commercial horticulture sector and private gardeners to reduce invasion risk from ornamental plants.","manuscriptTitle":"The introduced and invasive flora of Bermuda","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-10-10 16:35:09","doi":"10.21203/rs.3.rs-4958039/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2024-09-17T21:46:56+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-09-13T10:55:29+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Biological Invasions","date":"2024-08-31T18:31:41+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-08-31T11:28:47+00:00","index":"","fulltext":""},{"type":"submitted","content":"Biological Invasions","date":"2024-08-22T08:22:11+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"biological-invasions","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"binv","sideBox":"Learn more about [Biological Invasions](https://www.springer.com/journal/10530)","snPcode":"10530","submissionUrl":"https://submission.nature.com/new-submission/10530/3","title":"Biological Invasions","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"a92b44dc-a0cf-4ac0-8057-f93e45f31322","owner":[],"postedDate":"October 10th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-03-17T16:11:48+00:00","versionOfRecord":{"articleIdentity":"rs-4958039","link":"https://doi.org/10.1007/s10530-025-03559-8","journal":{"identity":"biological-invasions","isVorOnly":false,"title":"Biological Invasions"},"publishedOn":"2025-03-14 15:57:23","publishedOnDateReadable":"March 14th, 2025"},"versionCreatedAt":"2024-10-10 16:35:09","video":"","vorDoi":"10.1007/s10530-025-03559-8","vorDoiUrl":"https://doi.org/10.1007/s10530-025-03559-8","workflowStages":[]},"version":"v1","identity":"rs-4958039","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4958039","identity":"rs-4958039","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}