Specimens of Villarsia cambodiana (Menyanthaceae), the only tropical Villarsia species, were collected from Vietnam, where the species had not been recorded. Molecular data were used to evaluate the phylogenetic position of V. cambodiana relative to 31 other Menyanthaceae taxa representing 11 species of Nymphoides and every species of Liparophyllum, Menyanthes, Nephrophyllidium, Ornduffia, and Villarsia. Phylogenetic analysis of nuclear (ITS) and chloroplast (matK/trnK, rbcL) DNA data strongly supported the resolution of V. cambodiana within Nymphoides, sister to N. aurantiaca. After plotting morphological data onto the molecular phylogenetic tree, we observed that leaf and inflorescence characters associated with an erect habit, which superficially would assign V. cambodiana to Villarsia, have arisen or been lost independently in several other Menyanthaceae species representing three genera. Moreover, several characteristics of this taxon, particularly seed morphology and an inflorescence with paired pedicels, are more consistent with those of Nymphoides than of Villarsia. We thus transfer V. cambodiana to Nymphoides under the new combination Nymphoides cambodiana.