Abstract
Previous floristic studies of Podostemaceae in Thailand recorded four species assigned to two genera in Loei Province, northeastern Thailand. Our explorations and taxonomic studies have resulted in six genera and 12 species from the Province, including four new species (Terniopsis heterostaminata, T. filiformis, Hydrobryum phurueanum, and H. varium), two new records to Thailand (H. vientianense and Polypleurum pluricostatum), two new records to Loei (Dalzellia kailarsenii and Thawatchaia trilobata), and new localities in Loei of the remaining four species. All species are strictly or moderately narrowly distributed, but H. japonicum is widely distributed. The species of Terniopsis differ from each other and from their congeners by the number of stamens, the length of the stamens relative to ovary, and the form of the stigmas. The new species of Hydrobryum are distinct in the caudate or acuminate long bract and in the long pedicel. Hydrobryum is the largest genus in Loei with six species. Four or five species occur densely in each of three rivers constituting a single river system in the Province. Loei is among the most species-rich areas in Thailand due to the mostly mountainous topography.
