INTRODUCTION

Pteridophyta (pteron = feather, phyton = plants), also known as ‘vascular cryptogams,’ are the most primitive vascular plants. The earliest of them appeared on the earth, in the mid-Paleozoic Era during the Silurian Period around 438 million years ago. The pteridophytes attained their peak of luxuriance during the Carboniferous and started declining in diversity and richness thereafter. Their decline continued with the evolution and dominance of flowering plants so much so what is left today of the primitive pteridophytes groups, many of them of arborescent nature that dominated the Carboniferous forests, are merely seven herbaceous living genera: Psilotum, Tmesipteris, Equisetum, Lycopodium, Phylloglossum, Selaginella and Isoetes, all being miniatures of their past. The development of xylem with woody elements for water conduction enabled the pteridophytes to be successful colonizers of drier lands, a big step forward from the amphibious bryophytes. These vascular plants evolved from the bryophytes, which may be called as the ‘amphibians of the plant kingdom’. The Bryophytes, mainly the mosses and liverworts, primarily lived in wet and humid conditions, and had no advanced conducting tissues like xylem or phloem. The arrival of pteridophytes, with specialized water and food conducting tissues, heralded an era of greater colonization of land surfaces, so much so many of them could attain great heights like the flowering trees. Yet the early pteridophytes had greater dependence on watery habitats, as during the Carboniferous Period, when the land was dominated by pteridophytes, the major groups of which the Lycophytes and Euphyllophytes, many of them attaining up to 40 m height, dominated swampy lands. When their golden era ended and the Carboniferous arborescent pteridophytes perished en masse these swamps were drained and the burial deposits of these ancient pteridophytes are today the major sources of coal.

The arrival and dominance of land during later times by gymnosperms and angiosperms found the near end of arborescent pteridophytes and greater desiccation of land surfaces, which required more superior water conducting elements in the xylem, which bulk of the ancient pteridophytes lacked. More diminutive pteridophytes co-evolved with gymnosperms and flowering plants, better equipped to live in drier conditions. Yet their prolific development happened in humid tropical forests in the shade and microclimatic conditions furnished by the modern forest ecosystems. Those of modern pteridophytes which can live independent of the microclimates of forests are mainly hydrophytic ones (like members of Marsiliales, Isoetales and Salviniales). Many others are annuals that come up gregariously on wet soils, damp walls and rocks etc. especially during the rainy season (eg. Ophioglossales, Selaginellales, Adiantales, etc.). The aquatic pteridophytes and the seasonal annuals seldom faced any threats as they could last as long as their wet habitats remain or the season of rains last. It is the others, a great number of species which are perennial pteridophytes that constantly require dampness and shade of forests, of stream-sides and of marshes and swamps that constitute the subject matter of this paper, the hygrophilous pteridophytes.

The pteridophytes, even the perennial ones, had to retain their evolutionary links with hydrologically rich habitats because of their fragile gametophytic generation which live independent of the dominant, larger sized sporophytic generations that are successful in colonizing drier landscapes. The male gametes produced by the gametophytes are ciliate requiring a watery medium to swim about for reaching the archegonium, inside which the female gamete is lodged. Therefore, understandably, to this day, the highest diversity of pteridophytes is found in the humid tropics, their numbers in general declining with increasing latitudes because of pronounced seasonality of climates. In the light of these generalizations on the water-relationships of pteridophytes, reviewing their distribution in Western Ghats, and particularly based on field studies in the central parts of this mountain range, this paper highlights the importance of conserving all hydrologically significant natural habitats for conservation of especially perennial pteridophyte diversity. Pteridophytes have highest speciation in moist tropical forests, followed by temperate regions and their decline in diversity is more pronounced with further increasing latitudes. Each fern species has its own preferences for temperature, humidity, soil type, moisture, etc. Admitting the need for much more rigorous work needed to substantiate the microclimatic requirements of pteridophytes, the importance of moisture conditions, apparently is the most singular decisive criterion for high diversity of perennial land pteridophytes in any given region. The range of habitats sheltering pteridophytes include fresh water bodies, including marshes and swamps, even mangrove swamps, forest floors and edges, alongside perennial streams, deep ravines and gorges, grasslands and cultivation areas of various crops, specially of tea, coffee and cardamom.