Abstract
Tree ferns are a remarkable group among the lycophytes and ferns. Geographical isolation is suggested as one of the main reasons for local endemism of tree ferns and the island of Sri Lanka has been identified as one of the best demonstration sites to observe this phenomenon. Despite its small size, Sri Lanka has a rich diversity and one of the highest levels of endemism of tree ferns in Asia. Their diversity here is considered as an unique and important gene pool in the world. The present eco-spatial survey is to study the diversity and ecology of tree ferns in Sri Lanka. The study identified nine tree fern species including one new record of an adventive species. The species are Cyathea hookeri, C. sinuata, C. sledgei, C. srilankensis, C. walkerae, C. crinita, C. gigantea, C. australis and Dicksonia antarctica. Of these, the first five species are endemic to Sri Lanka. Dicksonia antarctica and Cyathea australis are exotic and naturalised in forest clearings in Piduruthalagala forest. Cyathea hookeri, C. sinuata, C. sledgei and C. srilankensis are confined to limited populations in lowland rainforests (62-550 m). Cyathea walkerae is distributed in a wide elevational range throughout the wet zone (30-2,300 m), whereas C. crinita shows a restricted distribution pattern at a high altitude range (1,800-2,400 m). In this study C. gigantea was recorded additionally from lowland rain forests, though it was previously reported to be confined to submontane and montane ecosystems. The results of this study provide baseline information on the distributional ecology of Sri Lankan Cyathea species. It will be useful to assess their current conservation status and to formulate conservation guidelines for these remarkable and spectacular ferns so characteristic to Sri Lanka.
Highlights
Tree ferns are usually placed in two families namely, Cyatheaceae and Dicksoniaceae, which are both ancient families placed relatively early in taxonomic classifications and from among which several major modern lineages of ferns are derived
The results of this study provide baseline information on the distributional ecology of Sri Lankan Cyathea species
This study identified seven native tree fern species (Cyathea hookeri, C. sinuata, C. sledgei, C. srilankensis, C. walkerae, C. crinita and C. gigantea), including five endemic species and two adventive species (C. australis and Dicksonia antarctica)
Summary
Tree ferns are usually placed in two families namely, Cyatheaceae and Dicksoniaceae, which are both ancient families placed relatively early in taxonomic classifications and from among which several major modern lineages of ferns are derived. The family Cyatheaceae has a wide pan-tropical geographical distribution combined with pronounced local endemism (Tryon and Gastony 1975). It contains about 500 species worldwide with diversity centres in tropical rain forests (Holttum, 1963, 1965, 1981; Conant et al 1996; Tryon and Gastony, 1975). Cyathea srilankensis Ranil) are endemic to Sri Lanka and two species (Cyathea crinita (Hook.) Copel. Ex Hook.) Holttum) are native to the island and distributed elsewhere (C. crinita is only known otherwise from South India, and C. gigantea is a wide spread Malesian element in south and east Asia). There is considerable diversity in the island and the species present include a great range of remarkable morphological diversity
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