The high occurrence of dioecy on oceanic islands has attracted much attention from plant evolutionary biologists. Tournefortia argentea (Boraginaceae), an Indo-Pacific strand plant, has an unusual sexual system which remains poorly understood. Here, we investigated the sexual system of T. argentea based on morphological and micromorphological studies, as well as manipulated pollination treatments. Two morphs of plants were found in the natural populations on Xisha Islands: hermaphrodite and female plants. Each sexual morph exhibited different floral traits, showing a modest form of sexual dimorphism. Flowers of hermaphrodites display significantly larger size in corolla and anther than those of females. Fruit sets under natural condition and hand pollination in hermaphroditic individuals were both far lower than that of female ones, which shows characteristics of both leaky dioecy and gynodioecy. We investigated how these differences in floral traits between females and hermaphrodites affect the choice of pollinators. Although females and hermaphroditic flowers in T. argentea attracted the same assemblage of pollinator species, including Apidae, Syrphidae and Utetheisa lotrix (Arctiidae), the reduction in allocation to pollinator-attracting structures (corolla) and rewarding products caused a significant reduction in Apidae visitation to female flowers. Accordingly, T. argentea is another example of a gynodioecious species of flowering plants in Boraginaceae with clear sexual dimorphism occurring in oceanic islands. The sexual system in T. argentea may imply a transitional stage in the evolution to dioecy and may have been favored during colonization to newly reclaimed habitats, where mating partners may be limited.

中文翻译：

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Gynodioecy 或leaky dioecy？珊瑚沙丘居民 Tournefortia argentea (Boraginaceae) 的不寻常的性系统

海洋岛屿上雌雄异株的高发引起了植物进化生物学家的广泛关注。Tournefortia argentea (Boraginaceae) 是一种印度洋-太平洋地区的植物，它有一个不寻常的性系统，但人们对其知之甚少。在这里，我们基于形态学和微形态学研究以及操纵授粉处理调查了 T. argentea 的性系统。在西沙群岛的自然种群中发现了两种植物形态：雌雄同体和雌性植物。每个性变体都表现出不同的花特征，表现出适度的两性异形。雌雄同体的花在花冠和花药中的尺寸比雌性大得多。雌雄同体个体在自然条件下的坐果率和人工授粉率均远低于雌性个体，这显示了泄漏雌雄同株和雌雄同株的特征。我们研究了雌性和雌雄同体之间的这些花卉特征的差异如何影响传粉者的选择。虽然 T. argentea 中的雌性和雌雄同体的花吸引了相同的传粉物种组合，包括蜂科、Syrphidae 和 Utetheisa lotrix (Arctiidae)，但分配给吸引传粉媒介的结构（花冠）和奖励产品的减少导致蜂科的访问量显着减少到雌花。因此，T. argentea 是紫草科雌性雌雄同株开花植物的另一个例子，在海洋岛屿中出现明显的两性异形现象。T中的性系统。