HYDROLOGICAL AFFINITIES

The era of inventorisation of pteridophytes in central Western Ghats has, understandably, come to an end with the monumental work of Rajgopal and Bhat (1998), and it is high time that in future ecology and conservation are given greater importance. Our routine observations in the field, especially during forest ecological studies, and reviews of sporadic mention of pteridophytes habitats in literature bring to the fore the fact that among the most sensitive of the ferns, that are prone to early eliminations from their natural habitats, are the ones that are associated with very humid conditions (especially rainy season fern communities). The focus of this work is on gross affinities of pteridophytes with humid habitats. Figure 1 shows the similarity between the 8 different major habitats of pteridophytes based on species occurrence. The habitats can be divided into two major groups A (which includes Aquatic, brackish water habitat) and B (which includes remaining 7 habitats). Group A is totally different from group B and includes a mangrove fern (Acrostichum aureum), found growing gregariously in the tidal backwaters in the costal swamps and marshes; it is the only species of fern known so far growing in the brackish water environs of the State. Group B can be further sub-divided into two sub-groups viz. B1 (including Fresh water aquatic and amphibious habitats) and B2 (including remaining 5 habitats). Group B1 is mostly represented by those species which need extremely watery or marshy habitats and include some of the rare hydrophytic species such as Isoetes sahyadriensis and I. sampathkumarani which deserve greater attention from conservationists. Two of the aquatic ferns namely Marsilea minuta and Azolla pinnata falling in this group are found widely distributed in ponds, paddy fields and other fresh water wetlands in the plains and hills of the State. In stark contrast is Salvinia molesta, an exotic free-floating fern, has become a serious weed choking many water bodies. It is a fast growing plant usually found in ponds, lakes, paddy fields, etc. significantly affecting the aquatic flora and fauna. Group B2 is further sub-divided into three clusters – B2a (including stream banks and moist forests), B2b (including roadsides and rock crevices) and an intermediate cluster B2c (which includes the high altitude sholas and meadows). These habitats shelter most of the members of fern group – Filicales.

Figure 1: Similarity of different habitats of pteridophytes based on species occurrence in central Western Ghats

The fern group – Filicales is the largest group present on the earth today represented by almost 6000 species of ferns, most of which are mesothermal hygrophytes; that is, they flourish under moist conditions with moderate temperature, and the majority of them are shade loving plants. Of the perennial fern species preferring swampy/moist habitats for their growth include tree fern species Cyathea gigantea, Angiopteris indica and A. helferiana. Similarly, another endemic fern Osmunda huegeliana prefers the moist and humid banks of free flowing perennial streams and rivers. The filmy ferns belonging to family Hymenophyllaceae are strongly hygrophilous and their growth is restricted to wet and moist places, dense and dark forests with a relative constant high degree of humidity being their preferred habitats. Their delicate frond morphology has enabled them to grow as epiphytes in very humid regions (Dubuisson et al. 2003). It is probable that the absorption of water is mostly performed in them by diffusion through the filmy lamina (as in bryophytes; Hébant, 1977), less often by rootless stems and sometimes by specialized root-like shoots (Schneider, 2000). The hygrophilous habitat is prevalent in many ferns, so much so in some of them occur even in association with swamps. The endemic and threatened tree fern Cyathea nilgirensis has its habitat confined to the relic evergreen forests with rare kind of swamps and perennial streams. We found it in the Myristica swamps of Kathalekan (……), its northernmost limit of distribution in the Western Ghats. It occurred there along with rare trees such as Syzygium travancoricum (Critically Endangered), Dipterocarpus indicus and Myristica magnifica (both Endangered), Gymnacranthera canarica (vulnerable) and Semecarpus kathalekanensis (newly discovered rare tree)- all of them of hygrophilic nature in the latitude of Uttara Kannada, where the rainfall barely lasts six months. List of notable pteridophytes of central Western Ghats in relation to the eight different habitats related to various hydrological conditions is given in Table 2.

Table 2: Notable pteridophytes in relation to different habitats in central Western Ghats