Cyathea nilgirensis Holttum (Cyatheaceae – Pteridophyta)
: A threatened tree fern from Central Western Ghats
Sumesh N. Dudani1,2, Mahesh M. K2, Subash Chandran M. D1, T.V. Ramachandra1,*
1Energy & Wetlands Research Group, Center for Ecological Sciences [CES], Indian Institute of Science,
2Department of Botany, Yuvaraja's College (Autonomous), University Of Mysore, Mysore
Citation : Sumesh N, Dudani, Mahesh M. K, Subash Chandran M. D and Ramachandra T. V, 2014. Cyathea nilgirensis Holttum (Cyatheaceae – Pteridophyta): A threatened tree fern from Central Western Ghats , Journal of Threatened Taxa | www.threatenedtaxa.org | 26 January 2014 | 6(1): 5413–5416.
The Western Ghats of the Indian peninsula constitute one of the 34 global biodiversity hotspots along with Sri Lanka, on account of exceptional levels of plant endemism and by serious levels of habitat loss (Conservation International, 2005). It straddles through the states of southern Gujarat, Maharashtra, Goa, Karnataka, Tamil Nadu and Kerala, practically forming an unbroken relief dominating the west coast, for almost 1600 km from the mouth of river Tapti to the tip of South India. The complex physiography of the rugged mountain chain, the general elevation varying from 400-500 m to exceptionally high peaks exceeding over 2500 m, especially in the Nilgiris and Anamalais, and rainfall ranging from 1000-6000 mm are major reasons for rich biodiversity and high endemism. There are about 2015 endemic flowering plant taxa in Peninsular India, of which about 1600 are confined to the Western Ghats (Chandran et al. 2010). The overall latitudinal and altitudinal gradients, rainfall patterns brought in by the South-West and North-East monsoons, reduction in number of rainy months progressively towards northern latitudes and towards the leeward side of mountains and variations in soils and rocks coupled with over three millennia of vegetation changes caused by humans have resulted in a mosaic of ecological islands, niches and refugia favouring with varied degrees of endemism that reach highest in rare stands of relic forests having conservation histories since time immemorial.
Several studies have been carried out on flowering plants of Western Ghats. However, the lower vascular plants, and in particular pteridophytes did not receive much attention. Pteridophytes including ferns and fern-allies (Lycophytes) are the earliest of the vascular plants on the earth that heralded the arrival of an advanced vascular system – xylem for water and phloem for food transport respectively. They grow luxuriantly in moist tropical and temperate forests from sea level to the high mountains. The pteridophytes among the vascular plants with about 12, 000 species are next only to the angiosperms in the world. More than 1200 species of pteridophytes have been reported from India (Dixit, 1984; Chandra, 2000). However, due to the presence of many doubtful species this seems to be an overestimate and hence, the actual number of pteridophytes species are estimated to be 900-1000 (Chandra et al. 2008). Undulating terrains of Western Ghats hills are habitats for about 320 species of pteridophytes (Dudani et al. 2011).
Prospecting for rare vegetation and their specific kinds of habitats, based on flowering plant communities, might lead to the discovery of some rare ferns as well. For instance Cyathea crinita Copel., an Endangered tree fern is found only in the cooler shola and other high altitude (>1500 m) evergreen forests of southern Western Ghats especially alongside shaded streams (IUCN, 2012). Similarly, Lycopodium wightianum (Wall. ex Hook. & Grev.) Holub, a South Indian species, considered to be Near-threatened (Chandra et al. 2008), has its specific habitats in higher altitudes (1800-2400 m) on exposed slopes and grasslands (Manickam & Irudayaraj, 1992).
While studying some of the exclusive, threatened, swamps overgrown with wild nutmeg trees (Myristica swamps), in the Kathalekan forest of Uttara Kannada in central Western Ghats, several sensitive fern species were found in association with rare community of evergreen trees like Myristica magnifica Bedd. (Endangered), Dipterocarpus indicus Bedd. (Endangered), Gymnacranthera canarica (King) Warb. (Vulnerable), Syzygium travancoricum Gamble(Critically endangered), Semecarpus kathalekanensis Dassapa & Swaminath (newly discovered tree species of mango family, assigned to Critically Endangered status) and scores of other canopy and understory endemic flowering plants. Mention may be made of South Indian endemics like, Bolbitis subcrenatoides Fras.-Jenk., B. semicordata (Bak.) Ching and others like the tree fern Cyathea gigantea (Wall. ex Hook.) Holttum, Pteris quadriaurita Retz., Leptochilus axillaris (Cav.) Kaulf, etc. Among the many climax forest relics, Kathalekan (Kathale = dark; kan = sacred forest) relic forest in Uttara Kannada District, of Central Western Ghats in Karnataka is with the repository of rare biotaevident from 35 species of amphibians from an area of 2.25 km² (Chandran et al. 2010).
Cyathea nilgiriensis Holttum, a South Indian endemic tree fern (Fraser-Jenkins, 2008) was seen growing in the deep shade of the swampy forest of Kathalekan in the Uttara Kannada. This is a new report of its distribution anywhere from north of 14° latitude in the Western Ghats. The tree ferns of the genus Cyathea belong to the family Cyatheaceae which has 241 species and 4 hybrids distributed throughout the mountainous regions of the world (Khare & Srivastava, 2009). India has 11 species of Cyathea (Dixit, 1984) of which C. nilgirensis was listed ‘Endangered’ (IUCN, 1998), but subsequently brought into the category of ‘Least Concern’ (IUCN, 2012).
Chandra et al. (2008) have carried out extensive work on the distribution and nomenclature of pteridophytes in India and consider the threat categorization by IUCN of the pteridophytes of India are based on often erroneous names, taxonomic misunderstandings, and insufficient studies on distribution. This has necessitated a fresh look on this subject. As Chandra et al’s is a convincingly good approach towards threat categorization, until a revision happens in IUCN’s Red Listing of Indian pteridophytes and as a lone population of few individuals of C. nilgirensis survives precariously in the threatened swamps of Kathalekan in Uttara Kannada, the northernmost range of its distribution in the Western Ghats, we felt it reasonable to endorse its Near Threatened status.
Image 1. Kathalekan Sacred grove in Uttara Kannada District,
The fern is also, notably, listed in the Appendix-II of CITES (Convention of International Trade in Endangered Species of Wild Fauna and Flora) (Sanjappa & Lakshminarasimhan, 2011). It is distributed in restricted pockets in the shaded and damp streamside forests of Kerala, Karnataka, Tamil Nadu and Andhra Pradesh. It was reported from Kemmangundi and Charmadi Ghats of Chikmagalur district, Mercara – Bhagamandala – Talacauveristretch in Kodagu district and in Sakleshpur and Devalkere in Hassan district (Rajagopal & Bhat, 1998) and now from south of Uttara Kannada, Central Western Ghats. In Kathalekan the species exists precariously, with merely four individuals left, obviously the last relics of what would have been once a primeval forest before the introduction of agriculture and forestry operations by humans.
Image 2. Threatened tree fern Cyathea nilgirensis Holttum in the
swamp forest of Kathalekan
Cyathea nilgirensis Holttum in Kew Bull. 19: 468. 1956; Nayar & Kaur, Comp. (syn.: Alsophila nilgirensis (Holttum) R. Tyron) is noted for un-branched trunk of 2-4 m height, 12-13 cm in diameter; bearing crown of fronds at the apex and scales densely covering the younger fronds. Stipes swollen at base, bearing small hairs. Lamina bipinnate, oblong-lanceolate, pinnae about 12 pairs, alternate, distinct petiolate, pale green below, dark green above, texture herbaceous. Pinnules acuminate, margin pinnatifid up to the costa; ultimate lobes about 15 pairs, alternate, oblong, 1.5 x 0.4 cm, margin crenate. . Sori situated on the vein forks of the lower half of the segments, exindusiate, paraphyes intermingled with sporangia, spores trilete. Grows as terrestrial species along shaded stream banks (Manickam & Irudayaraj, 1992). This can be easily differentiated from the other commonly occurring species C. gigantea which has a characteristic “V” shaped soral arrangement in each pinnule lobe and margin of pinnae lobed 2-5 mm towards the costa.
C. nilgirensis prefers habitat with relatively higher moisture content such as Myristica swamp. With their little known biota, the Myristica swamps are virtually live museums of ancient life of great interest to biologists. Such swamps of high watershed value and evolutionary significance (the Myristicas are considered among the most primitive flowering plants) have been practically on the road to extinction due to neglect and need for industrial softwoods and agricultural expansion. These swamps were reported for the first timefrom the Travancore region (Krishnamoorthy, 1960) and classified under a category called ‘Myristica Swamp Forests’ under the sub-group 4C by Champion & Seth (1968). The dipterocarp forests of Kathalekan, laced with Myristica swamps were considered significant areas for conservation because of their primeval characters (Chandran & Mesta, 2001; Chandran et al. 2010). Over the last few centuries, most of the Myristica swamps that normally occur along sluggish streams in primeval forests favored habitats of ferns like C. nilgirensis, have unfortunately given way to secondary forests, savannas, monoculture tree plantations, cash crops such as tea, coffee, arecanut and rubber, rice fields etc. (Chandran & Mesta, 2001; Gururaja et al. 2007).
The swamps of Kathalekan are seriously threatened habitats because of stream diversions to adjoining cultivation areas, depriving many downstream species including the sensitive fern community of the much needed water for summer survival. Trampling of ground vegetation by domestic cattle from adjoining villages has suppressed the regeneration of the tree ferns. Moreover, the proposed widening of Honavar – Bangalore National Highway passing adjacent to Kathalekan could as well be disastrous to tree ferns including C. nilgirensis, some of the last relics of the Mesozoic tree ferns.
The Biodiversity Act (2002), of the Government of India has provisions enough to declare such important biodiversity areas like Myristica swamps with their endemism rich biological community as ‘Biodiversity Heritage Sites’. However the initiatives are yet to be taken by the State Biodiversity Board and the Forest Department of Karnataka. The Department however has taken some steps to remove encroachments from swamps while also creating awareness on these threatened habitats and making efforts to restore swamp habitats through involvement of scientists and local village communities. Such actions, if coupled with introduction of the seedlings of these ferns in suitable habitats and botanical gardens and attempts to conserve the germplasm of it through mapping and conservation of all its habitats and application of tissue culture techniques for its rapid multiplication can be definitely helpful for the future of this fern.