Gynochthodes boninensis is a woody climber endemic to the Bonin Islands, Japan. It is characterized by an androdioecious sexual system, which is rare in angiosperms. We conducted a molecular phylogenetic analysis of 29 taxa including 61 samples from the tribe Morindeae to elucidate the geographical origin of G. boninensis by determining its progenitor species. We also investigated evolutionary transitions among different sexual systems within this plant group. The combined ETS, ITS, and trnT-F sequence data showed that G. boninensis formed a monophyletic group, but it did not form a clade with G. umbellata, which was treated as the same species, whereas it formed a clade with G. parvifolia, which is distributed in southeastern Asia. This suggests that G. boninensis evolved independently from G. umbellata, and probably originated from a progenitor native to southeastern Asia. In the clade composed of the three species of G. boninensis, G. parvifolia, and G. umbellata, only G. boninensis is androdioecious, whereas the others are dioecious. Thus, the androdioecious sexual system of G. boninensis may have evolved from dioecy., (Copyright © 2013 Elsevier Inc. All rights reserved.)