New Species and New Records of Podostemaceae from Phitsanulok Province, Northern Thailand

Previous studies recorded two genera and three species of Podostemaceae from a single river in Phitsanulok Province, northern Thailand. Recent extensive field research resulted in finding six additional species, i.e., two new species (Dalzellia sparsa and Hydrobryum mandaengense) and four new records for the province (Terniopsis minor, Thawatchaia trilobata, Hy. phetchabunense, and Hy. tardhuangense). Dalzellia sparsa is characterized by the various leaves on the cupule, and Hy. mandaengense has disporangiate anthers with tortuous dehiscence. In total, five genera and nine species (five of which belong to Hydrobiyum) occur in the province, with the result that Phitsanulok is the second most species-rich province, next to the adjacent Loei, for Thai Podostemaceae. Eight of the nine species known from the province are endemic to Thailand; Hy. tardhuangense occurs also in Laos. Among the endemics, D. sparsa, Hy. bifoliatum, Hy. kaengsophense and Hy. mandaengense are restricted to one or two river systems in Phitsanulok; the remaining four species occur widely. The descriptions of Hanseniella heterophylla, Hy. phetchabunense, and Hy. tardhuangense is emended using new collections. A key to all 49 species of Thailand has been updated.