Evolution of sexual systems in Gynochthodes umbellata and its allies (Rubiaceae)

伞花Gynochthodesumbellata（Rubiaceae）在有性系统上具有居群间的分化。分布于小笠原群岛的居群具有被子植物中罕见的雌雄异株性系统，而分布于琉球群岛的居群则为雌雄异株。本文从植物遗传学和传粉生态学的角度，探讨了该植物群内不同有性系统之间的进化转换，以及与这些不同系统相关的生态因素。遗传学分析表明，小笠原群岛的雌针蟹种群与琉球群岛的种群没有形成一支，表明它们之间的亲缘关系较远。小笠原种群的雌雄异株性系统可能是从雌雄异株进化而来的，因为小笠原种群的近缘种包括小笠原。伞形科植物和它的盟友是功能雌雄异株的

Gynochthodes umbellata (Rubiaceae) is differentiated among populations in sexual system. The populations occurring in the Bonin Islands are characterized by an androdioecious sexual system, which is rare found in angiosperm, while those distributed in the Ryukyu Islands are dioecious. I investigated the evolutionary transitions among different sexual systems within this plant group, and the ecological factors associated with these different systems from the viewpoint of phylogenetics and pollination ecology. The phylogenetical data showed that the Gynochthodes populations in the Bonin Islands did not form a clade with the populations distributed in the Ryukyu Islands, suggesting that they are distantly related each other. It was also suggested that the androdioecious sexual system found in the Bonin Island populations may have evolved from dioecy, since the related species including G. umbellata and its allies are functionally dioecious