Molecular species delimitation reveals underestimated diversity in the tree genus Nothapodytes (Icacinaceae)

Nothapodytes (Icacinaceae) is a genus of seven to eleven evergreen or deciduous tree species distributed in tropical Asia from India to Japan. Nothapodytes nimmoniana sensu lato is the most widespread species of the genus, being reported sporadically throughout South Asia, Southeast Asia, Taiwan, and Japan’s southwest islands. Nothapodytes amamianus was recently described from Amami-oshima, Japan, the northeastern edge of this widespread species’ range. However, the phylogenetic distinction between these two species has yet to be explored. Here we present an analysis of molecular species delimitation to test the morphology-based taxonomic hypothesis currently used to differentiate the two species. The results clearly show that N. nimmoniana sensu lato comprises two species, one in India and the other in Taiwan and Japan, including N. amamianus, requiring a reassessment of the morphological traits hitherto used to define the former and distinguish it from the latter in East Asia. Based on the taxonomic history of the taxa and rules of nomenclature, the name N. nimmoniana is retained for the former. We propose a new combination, N. insularis, for the latter. Longitudinal intraspecific geographic structure is highlighted as an apparent indicator of further hidden diversity in India’s Western Ghats.