The study of vascular plant diversity in the Bonin Islands including Mukozima-Retto and Kazan-Retto

博宁群岛由大约20个小岛组成，然而，植物区系和进化研究主要在千岛岛和Hahajima岛进行，因为很难访问其他偏远的Mukojima-Retto岛和Kazan-Retto岛。这项研究的目的是了解这些偏远岛屿的植物区系，并估计本土植物物种多样化的过程和因素。证实了大量野生山羊对Mukojima-Retto岛的Mukojima和Nakodjima维管植物区系造成的巨大破坏。近年来，所有的山羊都被根除了，然而，以前的植物区系名录中报告的许多分类群都不见了，还有几个非本土植物物种受到了干扰。与Mukojima-Retto相比，喀山-Retto的Kitaiojima植物区系保存得很好，但一些外来入侵植物物种，如无花果，一直在蔓延。为了解决海洋岛生物群的保护问题，我们对外来物种的影响进行了研究，对海岛的物种形成进行了形态和分子方面的研究，如木槿属、木槿属和波尼尼亚属。这些研究表明，这些植物物种的种群结构源于与之相关的生态分化。分别从植被类型、种子传播方式和花期转移对基因流动的限制三个方面研究了博宁特有植物及其近缘种的性别差异。博宁地方性假性维克斯特罗被发现为雌雄异株，它似乎是从群岛内的两性祖先进化而来的。此外，我们还观察到海棠Morinda umellata subsp.博尼虫和同精木霉属可能分别是雄雄异株和异花柱。

The Bonin Islands consist of about 20 small islands, however, floristic and evolutionary studies had been conducted mainly in Chichijima and Hahajima islands, because of the difficulty to visit the other remote islands of Mukojima-Retto and Kazan-Retto. The aim of this study is to get in touch with the flora of these remote islands and to estimate the processes and factors of diversification for native plant species.The vascular flora of Mukojima and Nakodojima in Mukojima-Retto, which had been caused a great deal damage by a large number of feral goats, was confirmed. All of the goats were eradicated in recent years, however, many taxa reported in previous flora list were missing, and several non-native plant species have been irrupting. The flora of Kitaiojima in Kazan-Retto has been well preserved in comparison with Mukojima-Retto, but some invasive non-native plant species such as Ficus microcarpa have been spreading. We have studied about the impact caused by non-native species, in order to address the conservation problems for oceanic island biotas.Morphological and molecular studies to infer the speciation in oceanic islands have been progressed for genus Syzygium, Hibiscus and Boninia. These studies suggested that population structures of the plant species have been derived from ecological divergence associated with. vegetation types, mode of seed dispersal and restricted gene flow by shift of flowering periods respectively.The sexual differantations were studied for the Bonin endemics and the relatives. The Bonin endemic Wikstroemia pseudoretusa was founded to be dioecious, and it seems to evolve from the hermaphroditic ancestor within the Islands. Furthermore, we also observed that Morinda umbellata subsp. boninensis and Psychotria homalosperma are probably androdioecious and heterostylous respectively.