Taxonomic diversity of green plants (Viridiplantae) in the Caatinga Phytogeographic Domain: a study supported by environmental licensing

The limited access to taxonomic and biogeographical data on plants across large spatial scales poses challenges for biodiversity researches. Our study explored richness, taxonomic contributions, and biogeographic insights linked to a floristic inventory spanning 56,144 km² of the Caatinga Phytogeographic Domain (CPD), supported by environmental licensing of a water infrastructure project (São Francisco River Transposition Project - PISF). Over fifteen years, we collected specimens of several plant groups (algae, angiosperms, bryophytes, ferns, and lycophytes), compiling taxonomic, ecologic, and biogeographic data of the species in the study area (e.g. threat status, life form, geographic origin, endemism for CPD) which resulted in the checklist and a biodiversity dataset. We compared our number of plant samples or species richness in the study area to the numbers previously known for this area. We used rarefaction curves to asses the increase in species richness in the study area as the number of plant samples increased. We collected 29,247 samples and identified 1,610 species. Herbaceous plants were the dominant group, comprising 40.89% of the species richness. We documented 173 species endemics to the CPD and 16 species mentioned on the Brazilian national list of threatened species. Additionally, our study recorded 284 first occurrences of 110 species in one or more states in the Northeast of Brazil or within the CPD. Collaboratively, we described two new species with specialists, and the donation of duplicate samples to national herbaria resulted in the citation of five paratypes. Our checklist increased the number of specimens previously recorded in the study area by 240% and expanded species richness in this area by approximately 14%. The rarefaction curve computed with our dataset indicated a trend toward stabilization of species numbers in the study area. These findings underscore the importance of primary data from environmental licensing associated with infrastructure projects in addressing gaps in biodiversity knowledge.