Phylogeographical studies on the origin and evolution of plants in the Bonin Islands, Japan

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In the present study, we conducted a molecular phylogeographic analysis of several taxa to elucidate the geographical origin of the species occurring in the Bonin Islands, Japan. We collected several plant materials from the Bonin Islands and its surrounding areas, such as the Ryukyus, Taiwan, the Philippines, Guam, and the Hawaiian Islands. Our phylogenetic results showed that Gynochthodes boninensis (Rubiaceae), endemic to the Bonin Islands is most closely related to G. parvifolia from Taiwan rather than G. umbellata, which was treated as the same species as G. boninensis. This result suggests that G. boninensis may have originated from a progenitor native to eastern Asia. Gynochthodes boninensis is reported to have an androdioecious sexual system, which is rare in flowering plants, whereas its closely relatives, G. parvipolia and G. umbellata are dioecious. The androdioecious sexual system of this species may have evolved from dioecy.