An updated account of Adiantum (Pteridaceae: subfamily Vittarioideae) in Thailand

An updated account of Thailand's maidenhair ferns, Adiantum L. (Pteridaceae), is presented. The genus consists of 20 taxa, including 19 indigenous and 1 naturalised, distributed in various habitats throughout Thailand, and 5 of them are endemic. We accept A. fragiliforme and A. ciliatum as distinct species on the basis of our investigation. We also accept infraspecific taxa within A. philippense, namely A. philippense subsp. philippense and A. philippense subsp. intermedium. Revised descriptions of A. fragiliforme and A. gomphophyllum from southern Thailand are provided, as is an updated key to the species of Adiantum in Thailand, and vernacular names and conservation status assessments.