Exploring Spore Morphology in Pteridophytes of The Nilgiris, Western Ghats, Tamil Nadu, India

Understanding the morphology of pteridophyte spores provides fundamental information needed to study their biological distribution patterns. The present study investigates pteridophyte spore morphology by studying physical traits including structure dimensions in addition to shape features and colour variations and surface markings. A taxonomic examination reveals that observed spores belong to two different groups that either demonstrate advanced monolete morphologies or primitive trilete characteristics with individual spore measurements ranging between 15 µm and 150 µm. Clusters of Pyrossia porosa megaspores reached the largest dimensions at 70×95 micrometers whereas Polystichum aculeatum possessed the smallest spores sized at 21×26 micrometers. Surface ornamentation in spore structure mainly depends on exine and perine. Researchers detected numerous surface ornamentations as reticulate, regulate, cristate, folded, granulate, perforate, rugate, tuberculate and verrucate patterns. Median monolete advanced morphology was observed in 29 out of the 35 plant species identified during the study although trilete basic morphology was found in twelve different species. The systematic importance of features derives from spores in fern classification \received DD MMMM YYYY \acceptedDD MMMM YYYY Exploring Spore Morphology in Pteridophytes of The Nilgiris, Western Ghats, Tamil Nadu, India \received DD MMMM YYYY \acceptedDD MMMM YYYY Abstract Understanding the morphology of pteridophyte spores provides fundamental information needed to study their biological distribution patterns. The present study investigates pteridophyte spore morphology by studying physical traits including structure dimensions in addition to shape features and colour variations and surface markings. A taxonomic examination reveals that observed spores belong to two different groups that either demonstrate advanced monolete morphologies or primitive trilete characteristics with individual spore measurements ranging between 15 µm and 150 µm. Clusters of Pyrossia porosa megaspores reached the largest dimensions at 70×95 micrometers whereas Polystichum aculeatum possessed the smallest spores sized at 21×26 micrometers. Surface ornamentation in spore structure mainly depends on exine and perine. Researchers detected numerous surface ornamentations as reticulate, regulate, cristate, folded, granulate, perforate, rugate, tuberculate and verrucate patterns. Median monolete advanced morphology was observed in 29 out of the 35 plant species identified during the study although trilete basic morphology was found in twelve different species. The systematic importance of features derives from spores in fern classification. Nilgiris hills, Perine, Pteridophyte, Spore morphology, Ughagamandalam

The Nilgiris region is located in the Western Ghat Mountains at 11.41° N 76.70 ° E. The region is surrounded by high peaks with a diverse array of fern and their allies (Shah and Kumarasamy, 2021). Udhagamandalam (Ootacamund) serves as the designated appellation for Ooty. Udhagamandalam, abbreviated as Udhagai) is a town and municipality in the district Nilgiris of Tamil Nadu, India. Udhagamandalam located in Nilgiri hills, named for Kurunji flower that blooms every twelve years adorning the slopes a bluish tinge. Snowdon, Elk Hill, Doddabetta, and Club Hill are the four mountain ranges that surround Udhagamandalam, with Doddabetta being the second highest peak in South India. The jurisdiction of Udhagamandalam encompasses an area of 36 square kilometres, with its forests extending over a significant portion of the realm’s land area. The southwestern part of India contains 1,300 distinct species of ferns which are scattered among 70 families and 191 genera throughout its diverse bio-geographical regions according to Chandra et al. (2008). The Himalaya, western Ghats and Eastern Ghats serve as the principal focal points of fern distribution (Dixit, 2000). Fraser-Jenkins et al. (2017) report India hosts 1157 species of Pteridophytes (43 exotic species included) besides nearly 100 sterile hybrids. A substantial diversity of Pteridophytes reaches over four hundred types in Southern India (Singh and Upadhyay, 2010). Studies of spore characteristics prove vital to taxonomy research as well as phylogenetic investigations. Devi (1977) established spore morphology as a fundamental taxonomic element to determine fern phylogenetic relationships. The classification work across all fern groups benefits strongly from the efficient nature of palynological data (Yea et al., 2000). The jelly-like perine structure shows flexibility while covering spores briefly and represents a specific fern adaptation for diverse amphibian environments (Schneider & Pryer 2002). Spore protection against desiccation exists as an advanced trait. Perine structures act as protective agents that guard fern spores against desiccation while showing their distinct role in spore evolutionary development. This paper aims at 1) Identification of the surface pattern of the spores, 2). Analysing the morphological characters of spores of pteridophytes, 3) Characterization of fern species through their spore ultrastructure and morphology.

The present study covered most of the fern species of the Nilgiris hills area of the Western Ghats from February 2020 to January 2021. Fern and allied plant identification helped researchers categorize the 35 studied species through herbarium methods using literature from Beddome (1892) and Manickam & Irudayaraj (1992). The Department of Botany at Annamalai University, Chidambaram, Tamil Nadu, India received complete sets of voucher specimens as part of standard preparation methods for species identification. Herbarium specimens were also deposited during this process. Researchers obtained fern spores directly from the living plants growing in the field. A microscope analysis of spore features including shape, size, color and surface was performed by cleansing spores with 95% alcohol before mounting them in glycerine jelly. Nairs Method (1970) allowed the use of Acetolysis for spore examinations under a light microscope. Using Devi (1977) and Elzbieta (2012), spore measurements recorded the Polar axis ’P’ length times Equatorial axis ’E’ length (in µm) by calculating mean values from ten observations per test sample. Following Erdtman’s proposed categorization system (1957) the spore dimensions were assigned. The classification scheme developed by Erdtman in 1957 served to determine the spore measurements. Spore measurements used micrometry on the 10X light microscope system. The characteristics of spores are described through palynological terminology based on Punt et al. 2007. The examinations were conducted by inspecting samples and the Olympus-CX21 Research Microscope at 40X and 100X magnification captured photographs of these samples.

and Discussion The present investigation recorded the spore morphology of different pteridophyte species collected from the Nilgiris Hills as follows. Pteridaceae Adiantum capillus- veneris L. Spores trilete, shape tetrahedral, size 40 × 55 μm, colour brownish, spore appears plano convex with rounded angle in lateral view and elliptic in polar view. Exine thin, smooth, perine absent (Fig. 3.1). Adiantum hispidulum Swartz in Schrader Spores trilete, shape triangular, size 35 × 42 μm, colour brownish yellow. Exine granulate (Fig. 3.2). Adiantum venustum D. Don, Prod. Spores trilete, shape triangular, size 33 × 40 μm, colour brownish yellow. Exinse 2 μm thick and mildly granulose (Fig. 3.3). Dryopteridaceae Arachniodes aristata Frost. F. Spores are monolete, shape bilateral, ellipsoidal, size 53×50 µm, colour brown, Exine granulose (Fig. 3.4). Arachniodes palmipes (Kunze) Fraser- Jenk. Spores monolete, Shape ellipsoidal, bilateral, size 51×49 µm, exine surfaces granulose (Fig. 3.5). Aspleniaceae Asplenium hindusthanensis Bir. Spore monolete, shape ellipsoidal, colour dark-brown, 26 × 28 µm, reticulate surfaces (Fig. 3.6). Asplenium nidus L Spores monolete, shape triangular, size 27 × 28 μm colour brown. Exine is loosely linked to the smooth perine (Fig. 3.7). Asplenium scolopendrium (Fernald) Kartesz & Gandhi. Spores monolete, shape bilateral, size 26 × 27 µm, colour dark brown. Exine reticulate to ornate, perine folded with a few spines and grains (Fig. 3.8). Athyriaceae Athyrium praetermissum Sledge Spores monolete, shape bilateral, bean shaped, colour light- brown, size 27 × 28 µm, and smooth perine (Fig. 3.9). Blechnaceae Blechnum occidentale var. minor Hooker. Spoaeres monolete, shape bilateral, size 22 × 32 μm, colour brown, spore appear as Plano convex in lateral view and elliptic in polar view. Exine 3 μm thick, low reticulate, perine is hyaline and thin (Fig. 3.10). Blechnum orientale L. Spores monolete , shape bilateral, size 22 × 32 μm, yellowish brown in colour. The appearance of Spores were plano convex in lateral view and elliptic in polar view (Fig. 3.11). Sinopteridaceae Christella dentata Forssk. Spores monolete, shape bilateral, ellipsoidal, size 36×24 µm, colour dark-brown, reticulate ridges (Fig. 3.12). Cyatheaceae Cyathea crinita (Hook) Copel. Spores monolete, shape tetrahedral, size 27 × 34 μm, colour light brown. The spores proximal half seems flat to slightly concave. Exine smooth to slightly granulate (Fig. 3.13). Cyathea nilgirensis Holttum Nayar & Kaur Spores monolete, shape tetrahedral, size 28 × 35 μm, colour light brown. The spore’s proximal half seems flat to slightly concave. Exine smooth (Fig. 3.14). Dryopteridaceae Cyrtomium caryotideum Wall, ex Hook & Grev. Spores monolete, shape bilateral, size 26 × 22 μm, colour yellow. Exine 4 μm thick, smooth perine strongly warty (Fig. 3.15). Cystopteridaceae Cystopteris fragilis L. Spore monolete, shape ellipsoidal, size 28 × 42 μm, colour brown. Exine coarsely echinate (Fig. 3.16). Davalliaceae Davallia griffithiana Hook. Spores monolete, shape bilateral, size 31 × 38 μm. Colour pale brown. Spores appear plano convex in lateral view and elliptic in polar view. Exine 2 μm thick, widely verrucate. Perine absent (Fig. 3.17). Gleicheniaceae Dicranopteris linearis Burm. F. Spores trilete, shape tetrahedral, size 24 × 32 μm. Colour light brown. Exine smooth. Perine is absent (Fig. 3.18). Blechnaceae Doodia dives Kunze Spores monolete, shape bilateral, size 23 × 31 µm, Colour brown and exine reticulate (Fig. 3.19). Pteridaceae Drynaria quercifolia (L.) J. Sm. Spores monolete, shape bilateral, size 42×63 µm, colour yellowish-brown, and surfaces spinulose to verrucate (Fig. 3. 20).Dryopteridaceae Dryopteris atrata Kunze. Spores monolete, shape bilateral, size 35 × 48 μm. Brown in colour, spores appear plano convex in lateral view and elliptic in polar view. Exine and perine smooth. Perine is folded into a series of small folds (Fig. 3.21). Dryopteris redactopinnata Basu and Panigrahi. Spores monolete, shape elliptic, brown in colour. Exine, the outer wall smooth or patterned in various ways. Spores are medium sized (Fig. 3.22). Pteridaceae Hemionitis arifolia (Burm F.) Moor. Spores trilete, shape tetrahedral, 36 × 35 μm, colour brown, exine thin, 1 mm thickness, delicate and smooth, while perine is smooth, loose, folds into irregular reticulations (Fig. 3.23). Lepisorus nudus (Hook.) Ching. Spores monolete, shape bilateral, size 48 × 71 μm. Colour brown. Exine conspicuously granulose. Perine not present (Fig. 3.24). Nephrolepidaceae Nephrolepis auriculata L Spores are monolete, shape bilateral, size 26 × 18 μm. Colour yellowish. Exine reticulate (Fig. 3.25). Nephrolepis multiflora Roxb. Spores monolete, shape bilateral, size 37 × 45 μm. Colour brown. Exine ornate or verrucate (Fig. 3.26). Ophioglossaceae Ophioglossum reticulatum L. Spores trilete, shape tetrahedral, size 30 × 23 μm. Colour light yellow. Exine ornamented with thick warts (Fig. 3.27). Pteridaceae Pellaea falcata R. Br. Spores monolete, shape bilateral, ellipsoidal, size 29×30 µ, Colour brown and surfaces rugate (Fig. 3.28). Pellaea rotundifolia G. Forst. Spores trilete, shape radio- symmetrical, size 31 × 28 μm. Colour yellowish brown. Exine thin, granulose (Fig. 3.29). Polypodiaceae Polypodium vulgare L. Spores monolete, shape bilateral, size 35 × 43 μm, colour yellow. Exine is verrucate (Fig 3.30). Dryopteridaceae Polystichum aculeatum L. Spores monolete, shape bilateral, size 21 × 26 μm, colour brown, spore appears plano- convex in adjacent view and elliptic in polar view. Exine 1 μm thick, smooth perispore, perine with many irregular folds (Fig.3.31). Polystichum paleaceum Borkh. Spores monolete, shape bilateral, size 38×31 µ, colour brown and perine smooth (Fig.3.32). Pteridaceae Pteris biaurita L. Spores trilete, shape tetrahedral, size 43-40 µm, colour blackish-brown. Exine tuberculate. Tubercles are smaller on the proximal surface than those on the distal surface (Fig.3.33). Pteris vittata L Spores trilete; shape tetrahedral, size 45 × 55 μm, colour yellowish brown. Exine 4 μm thick, irregularly tuberculate to regulose on the proximal surface and homobrochate on the distal surface (Fig. 3.34). Polypodiaceae Pyrossia porosa Havenk. Spores monolete, shape bilateral size 70 × 95 μm, colour brown. Exine 3 μm thick, conspicuously verrucate, perine not present (Fig.3.35). The morphological attributes of each species reported in the present investigation are tabulated in the table (Table 1).It is evident from the Table 1, that most of the trilete spores were tetrahedral and their amb. is triangular except the species Adiantum hispidulum, Pellaea falcata, and Pellaea rotundifolia,, while the monolete spores are mostly bilateral and appear reniform or ellipsoidal in amb. The majority of the spores were discovered to be medium or large sized. The spore size varied between the range of 15 and 130 µm. Our observation is in agreement with Tyron’s statement (1986) that spores of homosporous fern size is between 15 to 150 µm. The spore comprises exine and perine which are mainly responsible for the ornamentation of the spore surface. Spore surface ornamentations were reported to be reticulate, regulate, cristate, folded, granulate, perforate, rugate, tuberculate, verrucate etc. According to Bir (1977), trilete spores are found in Gymnogrammeoid, Adiantoid, Pteroid, Cyatheoid, Chelanthoid and Schizaeoid, groups while monolete spores were observed in Aspidoid, Athyroid, Blechnoid and Polypodiod ferns. The present investigation is in agreement with the Bir’s observation. Fern spore shapes were tetrahedral in 10 taxa (28 %), Triangular 3 taxa (8%), bilateral 22 taxa (62 %) Fig. 1 and their surfaces were smooth in 9 taxa, reticulate in10 taxa, verrucate in 6 taxa, echinate in 1 taxon, and granulate in 9 taxa respective. Conclusion The reproductive stage of 35 plant species was collected. So, the spore slides were prepared for 35 species. The result shows that the spores are classified in to two types viz., trilete and monolete. The Trilete spores were found in Adiantum, Cyathea, Dicranopteris, Hemionitis, Ophioglossum, Pellaea and Pteris. While as monolete spores were found in Arachniodes aristata, Arachniodes palmipes, Asplenium hindusthanensis, Asplenium nidus, Asplenium scolopendrium, Athyrium praetermissum, Blechnum orientale, Blechnum occidentale, Christella dentata, Cyrtomium caryotideum, Cystopteris fragilis, Davallia griffithiana, Doodia dives, Drynaria quercifolia, Dryopteris atrata, Dryopteris redactopinnata, Lepisorus nudus, Nephrolepis auriculata, Nephrolepis multiflora, Polypodium vulgare, Polystichum aculeatum, Polystichum paleaceum and Pyrossia porosa respectively. The variation in colour of fern spores was found. The spores reported in the present observation were mainly of brown colour while as with few exceptions yellowish spores ( Cyrtomium caryotideum, Lepisorus nudus, Pyrossia porosa and Pteris vittata ) were also reported. 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Authors Metrics & Citations Metrics Article Usage 377views 189downloads Citations Download citation Aadil Shah, Shagufta Rashid, Mohd Shahnawaz, et al. Exploring Spore Morphology in Pteridophytes of The Nilgiris, Western Ghats, Tamil Nadu, India. Authorea. 29 January 2025. DOI: https://doi.org/10.22541/au.173814483.37464616/v1 DOI: https://doi.org/10.22541/au.173814483.37464616/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. For more information or tips please see 'Downloading to a citation manager' in the Help menu.