Abstract
Two new diatom species from the Gomphonema subtile species complex were found in Đả Tiên reservoir, near the Town of Ðà Lạt, Lâm Đồng Province, Vietnam, as well as in the River Nam Leuk, Phou Khao Khouay, Laos. These new species include Gomphonema dalatica Glushchenko, Kulikovskiy & Kociolek sp. nov. and Gomphonema prowsei Glushchenko, Kulikovskiy & Kociolek sp. nov. Additionally, G. pantropicum Reichardt, a species known from the tropical zone, was found in our material. We provide light and scanning electron microscopical observations for all taxa, and offer formal descriptions for the two new species. Distribution of these three species is discussed.