On the pteridophytes of Bherjan-Borajan-Padumoni Wildlife Sanctuary , Assam , India

A preliminary survey on the pteridophytic flora of Bherjan-Borajan-Padumoni Wildlife Sanctuary of Assam, India revealed a total of 33 species belonging to 23 genera and 15 families. Most of the species belong to the family Pteridaceae followed by Polypodiaceae and Thelypteridaceae. A brief taxonomic description of each species is provided. Stenochlaena palustris (Burm.f.) Bedd., an edible fern, grows abundantly all over, especially in the openings and clearings.


INTRODUCTION
Pteridophytes, also known as ferns and fern-allies, flowerless and seedless plants that once dominated the world vegetation 280-230 million years ago. The main plant body is sporophytic and the dominant phase in its life cycle. Chapman (2009) estimates that there are about 12,000 species of ferns and fern-allies across the world. According to Moran (2015), "worldwide, there are about 13,600 species of ferns and lycophytes". According to a survey, the pteridophytic flora of India comprises around 1,000 species belonging to 191 genera and 67 families including 47 endemic Indian ferns (Dixit 1984) and in another report, more than 1,100 species of pteridophytes belonging to 144 genera and 34 families with about 235 endemic species (Chandra 2000) from India. According to Fraser-Jenkins et al. (2017), "altogether there are about 1135 species including 42 exotics and 53 further subspecies", from the Indian subcontinent.
The Bherjan-Borajan-Padumoni is one of the smallest wildlife sanctuaries of Assam covering 7.22 km 2 of area spreading across three blocks located in Tinsukia district of the Upper Brahmaputra Valley of Assam, India which consists of three separate forests, namely Bherjan, Borajan, and Padumoni. The forest is the home for an endangered primate species, i.e., Western Hoolock Gibbon. Bherjan, Borajan, and Padumoni are tiny isolated pockets of lowland tropical forest covering an area of 105 ha, 493 ha, and 176 ha respectively and an ideal habitat for primate species like the Bengal Slow Loris, Assamese Macaque, Pig-tailed Macaque, Rhesus Macaque, Capped Langur, Stump-tailed Macaque, and Western Hoolock Gibbon. The three areas are disjoint and unconnected by tea gardens and human settlement. These are entirely on the flat plains of the Brahmaputra Valley. There are small, scattered marshes, with swamps, covered with dense growth of grass and Alpinia herb. The natural vegetation of all these areas is tropical wet evergreen 'rainforest' type. Bherjan is almost entirely covered with trees with a closed canopy. The original vegetation has been replaced by a fairly old mixed plantation dominated by the deciduous species Lagerstroemia parviflora and Terminalia myriocarpa. The Padumoni part is mostly in a degraded state due to large-scale felling. The canopy has been very badly broken up. Only a few mature trees of Artocarpus, Bombax, Lagerstroemia, and Mesua species can be seen. Borajan is a pocket of excellent rainforest, dominated by Dipterocarpus macrocarpus. Except for Teak, all the species as in the other two forest pockets are found. Bamboo species are found in all areas.

METHODS
A number of field visits were undertaken to the study area in the year 2019-2020 ( Figure 1). The different pteridophytes were collected from a range of habitat; however, those species which are Red Listed (IUCN) or used as food or shelter were left untouched. Under such circumstances, digital photographs of the concerned species were taken. The specimens were preserved and studied with standard literature like Baishya & Rao (1982), Jamir & Rao (1988), and Borthakur et al. (2001Borthakur et al. ( , 2018. The plants were collected from the field, cleaned, and pressed for the preparation of herbarium. Herbariums are prepared by following standard herbarium technique (Jain & Rao 1977) and deposited at the Botany Department, Debraj Roy College, Golaghat, Assam. Digital photographs of the specimens were also taken and some of them are displayed (Image 1).
The families are enumerated in text according to Fraser-Jenkins (2009). However, the genera and species within the families are listed alphabetically. The taxonomic citation is based on published literature and IPNI, Tropicos, and The Plant List.

RESULTS
A total of 33 species of pteridophytes belonging to 23 genera and 15 families are recorded. The plants are enumerated with a brief taxonomic description of each species.
Epiphyte. Rhizome short creeping. Fronds without distinct stipe, simple, sessile, lanceolate or elliptic, base decurrent, margin entire, midrib across at the base, veins visible but not prominent; pinnae glabrous above and below, dark green when fresh, blackish when dry. Sori numerous, small, round, irregularly scattered on upper half of the frond; sporangia oval, short-stalked. Spores yellowish-green.
Climber. Rhizome long creeping, covered with black hairs. Stipes scaly at base. Fronds wide-spreading, tripinnate; primary pinnae forked, opposite; fertile pinnae much contracted giving an appearance of dissected lamina; texture herbaceous; primary rachis scabrous; secondary rachis ridged; veins distinct, free, reaching the margin. Sori finger like, marginal projections which are greenish when young and dark brown at maturity; sporangia short stalked, arranged in two rows, alternate. Spores small, numerous.
Terestrial. Rhizome long creeping, clothed with scales at the apex; scales ovate, acuminate at apex, margin entire. Stipes slender, sparsely scaly and black at the base, glabrous and brown above, adaxially grooved, abaxially flattened. Lamina elliptic-lanceolate, simple pinnate with an apical pinnae; lateral pinnae numerous, sessile or very shortly stalked, basal pinnae not reduced, rachis grooved and hairy; veins slightly distinct below and densely covered by long, soft acicular hairs, upper surface glabrous; lamina pale green; sori medial on the veins, in two rows, arranged in V-shaped; indusia reniform, hairy. Spores pale brown. Epiphyte. Rhizome creeping, densely scaly all over; scales, apex long acuminate, base broad, thin, transparent, brown. Stipes firm, erect, scaly at base, glabrous above, chestnut brown, tripinnatifid, deltoidlanceolate, apex acute or acuminate; apex acuminate, base cuneate; secondary pinnae up to 12 pairs, alternate, sessile or shortly stalked, margin deeply cut down to lobe nearly to the costules; margin sharply toothed or crenate; veins not conspicuous, uniform, free, not reaching the margin; lamina dark reddish-brown when dry, glabrous. Sori half cup-shaped, obliquely placed as regards the central veins in the tooth, submarginal, brownish; indusia tubular or half cup-shaped, as long as broad.

Blechnaceae
32. Blechnum orientale L.; Collection No. DRC-5087. Terrestrial. Rhizome creel, densely scaly, massive, linear-lanceolate, apex acuminate, shining, dark brown. Stipes tufted, erect, scaly at base, glabrous above, reddish-brown at the base, grey brown above. Lamina ovate to linear-lanceolate, apex acute, simple pinnate; costa grooved above, rounded below; veins slightly distinct, simple or forked once or two times, free; lamina pale green, glabrous above and below, glossy. Sori linear along either side of the costa, continuous nearly to the apex, dark brown; indusia narrow, firm with entire margin. Spores round to oval, translucent, yellowishbrown.
Climber. Rhizome scandant, long creeping, thick, sparsely scaly, often climbing on trees; scales ovate, apex acuminate, margin ciliated, dark-brown at the centre, pale-brown at the periphery. Lamina dimorphic; stramineous, glabrous, adaxially grooved, abaxially rounded; simple pinnate; pinnae 8-15 pairs, lanceolate, apex acuminate, hard, rachis similar to stipe; veins distinct, simple or rarely once forked, reaching the margin; lamina green, glabrous on both surfaces, shining. Fertile lamina borne at the distal part of the plant, more or less same size and shape with the sterile one, but pinnae much contracted. Sori densely covering the lower surface except midrib and the extreme apex; J TT sporangia large, stalked, crowded. Spores monoiete, pale-green, spinulose.

DISCUSSION
The vegetation of the study area is mostly dominated by the angiosperms. Out of the 33 species of pteridophytes, two species belong to fern-allies and 31 species belong to true ferns. The two species of fernallies belong to the family Selaginellaceae. Considering the habitat, 25 plants are terrestrial, seven plants epiphytic, and one aquatic (Figure 2). Among them, three species are trees, three species are climbers and remaining 27 species are either herbs or shrubs ( Figure 3). Three species namely Angiopteris evecta (G.Forst.) Hoffm., Cyathea spinulosa Wall. ex Hook. and Cyathea gigantea (Wall. ex Hook.) Holtt. are tree ferns. Microsorum pteropus (Bl.) Copel. is the only aquatic fern found there. Lygodium flexuosum (L.) Sw., Lygodium japonicum (Thunb.) Sw., and Stenochlaena palustris (Burm. f.) Bedd. are climbers. Cyclosorus interruptus (Willd.) H. Ito is grown abundantly in swamp areas. Pityrogramma calomelanos (L.) Link. is commonly called as silver fern due to its silver colour spores and found to be growing in the forest and also grow on stored bricks or nearby brick making industries. Epiphytic ferns Microsorum punctatum (L.) Copel. and Asplenium nidus L. are seen to be growing plentifully in tree trunks not only in the forest but also adjoining areas. Diplazium esculentum (Retz.) Sw. is widely used as vegetables in the nearby area. The fern species like Cyathea gigantea (Wall ex Hook.) Holtt. and Diplazium esculantum (Retz.) Sw. were observed to be taken as food by Trachypithecus geei during their study in Kakoijana reserve forest, Assam. However, no record traced the existence of this endangered primate species in the present study area. Due to the subsistence of other primate species including the endangered Hoolock Gibbons, these two fern species were kept unscathed and only digital photograph were taken.
The family Pteridaceae has the greatest number of genera, i.e. 5; among them, the genus Pteris has highest number of species. In India, the family Thelypteridaceae is represented by 80 species and 16 hybrids (Fraser-