Additions to the Podostemaceae of Thailand with Molecular Phylogenetic Relationships of Cladopus, Hydrobryum and Thawatchaia

In this paper, based on recent collections, we add three species of Podostemaceae to the flora of Thailand. First, Cladopus pierrei was newly recorded from Sa Kaeo Province, southeastern Thailand. Phylogenetic analysis showed that C. pierrei is a paraphyletic species, in which plants from Thailand have a sister relationship with C. doianus. The number of stamens of C. pierrei in Thailand and Laos varies between 1 and 2, i.e., 2 in one clade, 1 in another clade, and 1 or 2 in a third clade. Cladopus is characterized by variation in stamen number. Second is Hydrobryum chompuense sp. nov. collected in Phitsanulok Province, northern Thailand. Phylogenetically, it is sister to H. varium, but morphologically distinct in having 1-locular ovaries with the septum free from the ovary wall. The third, Thawatchaia laotica, which has been reported from northern Laos, was newly recorded from Chiang Mai Province, northern Thailand. As a result, 10 genera and 52 species of Podostemaceae occur in Thailand.