The genus Nymphoides Séguier (Menyanthaceae) in Taiwan is revised based on comparative morphological, palynological, and cytological studies. Five native taxa, N. aurantiaca (Dalzell) O. Kuntze, N. coreana (H. Léveillé) H. Hara, N. hydrophylla (Lour.) O. Kuntze, N. indica (L.) O. Kuntze, and N. lungtanensis S. P. Li, T. H. Hsieh & C. C. Lin, sp. nov., and a cultivated species N. peltata (Gmelin) O. Kuntze are recognized in this paper. The ornamentation of seed coat and chromosome number are good characters in separating the Taiwanese taxa. SEM micrographs of pollen grains and seed coat, chromosome number, a key to species, descriptions, and taxonomic notes are provided.