Historical biogeography of Sri Lankan mangroves

Mangroves are a group of genetically unrelated plant taxa of angiosperms that occur in inter-tidal habitats in sheltered tropical coastlines. Biogeographically, mangrove areas are categorized into two regions: Sri Lanka is situated in the Indo-West Pacific (IWP) region where the plant diversity is significantly greater than in the Caribbean, West Pacific and Atlantic regions (CWPA). More than half the number of mangrove plant species that are exclusive to mangrove areas in the IWP region occur in the Sri Lankan mangrove areas that cover only about 16,000 ha. Being located in the land-sea interface, identification of mangrove areas and plant taxa endemic to mangrove ecosystems is ambiguous as plants that occur in non-mangrove areas too occur in mangrove habitats. This paper presents an insight into aspects relevant to resolving this ambiguity. Accordingly, 24 true mangrove species and a hybrid have hitherto been reported from Sri Lanka, out of which two are reported only once by a single researcher. Processes pertinent to historical biogeography of mangroves in Sri Lanka are discussed in the light of current hypotheses and knowledge base.