Taxonomic evaluation of Nymphoides (Menyanthaceae) in eastern Asia

According to recent taxonomic treatments, up to 13 Nymphoides species exist in eastern Asia, with some species purported to be narrowly endemic. However, these treatments have largely covered rather limited geographic areas, whereas the genus can be found worldwide. In order to evaluate the global distinctness of currently accepted Nymphoides species in eastern Asia, we quantitatively examined their distinguishing morphological characters using information from published treatments and data from herbarium specimens. Out of 13 evaluated species, nine were found to be morphologically distinct (N. aurantiaca, N. cambodiana, N. coreana, N. hastata, N. hydrophylla, N. indica, N. lungtanensis, N. parviflora, N. peltata), and the remaining species (N. coronata, N. cristata, N. siamensis, N. tonkinensis) lacked characters that clearly could distinguish them. We thus propose that the morphologically indistinct species should be considered synonymous with other Nymphoides species. Herein we establish N. parviflora comb. nov., to accommodate the species that was heretofore known by the invalid name N. parvifolia. Lectotypes are designated for Limnanthemum calycinum, L. coreanum, L. coronatum, L. hastatum, L. kleinianum, and L. tonkinense, and neotypes are designated for Menyanthes hydrophylla and M. nymphoides.