Evidence of Sympatric Speciation in Cyathea sinuata Hook. & Grev. from Lowland Rainforests of Sri Lanka

Abstract

The family Cyatheaceae (tree ferns) is represented by a single genus, Cyathea, with eight taxain Sri Lanka where 75% are endemic to the island. An endemic Cyathea sinuata Hook. &Grev. is an unique species because it is the only known simple leaves tree fern among about600 Cyathea species in the world. An eco-geographic survey was conducted covering allpossible natural habitats of all Cyathea species in 12 administrative districts of Sri Lankaduring the period of two years. Morphological characters were recorded following thestandard developed by Janssen (2006) from a total of 60 individuals of Cyathea species.Twenty two morphological characters used to perform Cluster Analysis. A detailmorphological investigation was carried out on 23 individuals of C. sinuata and itsmorphotype collected from Sinharaja and Kanneliya MAB reserves, Runakanda and Beraliyaproposed forest reserves (FR) and Hiniduma FR.

Results of cluster analysis and dendrogram revealed that all species were separately grouped.Interestingly, C. sinuata is clustered into two sub groups. Sub group I (usual C. sinuata) andsub group II (morphologically different form of it). Sub group II can be easily differentiatedfrom usual C. sinuata by their dentate leaf margin, irregular or global shape crown withdrooping leaves, the number of veinlets, spore arrangement and number of pair of sporangia.Since those variations and current information are not adequate to determine the correcttaxonomic status of two sub groups, it is suggested that sub group II may be a morphotype ofC. sinuata. It is also suggested that this may be an initial step of the evolutionary process,although this morphotype was observed only from the population of Sinharaja and KanneliyaMAB reserves. Sri Lankan ferns show wide range of morphological variation mainly due toisland nature of the country and long period of geological isolation from mainland India.Therefore, continuous monitoring of morphotype of C. sinuata within their natural habitatswill further reveal information on sympatric speciation.