Molecular Phylogeny of Zeylanidium (Podostemaceae) Showing a New Cryptic Species from Thailand

Zeylanidium (Podostemaceae) comprises ribbon-like and crustose-rooted species in Asia, of which Z. lichenoides sens. lat. is widely distributed in Sri Lanka, India, Myanmar and Thailand. This study was conducted to clarify its relationships. In the matK phylogenetic tree obtained, plants of Z. lichenoides from northern Thailand were far from Z. lichenoides sens. str. and are separated as a cryptic species, Z. tailichenoides sp. nov. Zeylanidium tailichenoides is characterized by a 1-locular ovary and is quite similar with Z. lichenoides sens. lat. in other characteristics. The remaining Z. lichenoides sens. lat. is divided into Z. lichenoides sens. str. and three populations that we refer to as Z. 'lichenoides,' although morphologically all five are hardly distinguishable. Zeylanidium tailichenoides and one population of Z. 'lichenoides' are related independently to the crustose species.