摘要：
雄全异株是自然界罕见的繁育系统.通过野外观察和人工授粉实验对雄全异株植物流苏树传粉生物学特征及繁育系统进行研究.结果表明:流苏树的雄花与两性花的雄蕊发育过程基本一致,均能产生功能花粉粒.两性花的两个心皮原基愈合分化形成雌蕊,雄花的两个心皮原基愈合后形成一个空室并停止发育至整体退化.雌蕊先熟,柱头可授期长,花粉在花药开裂后具有活力,室温下,活力维持在10％以上约2周.流苏树靠风和昆虫(主要是蓟马和食蚜蝇)传粉.控制授粉30 d后,自然对照结实率为34.36％;两性花不存在无融合生殖现象,自交亲和,但自发自交的结实率仅10.70％;人工授粉下杂交结实率显著高于自交(同株异花);有性生殖受到传粉者限制;是混合交配系统.证实流苏树是木犀科又一功能性的雄全异株,其依靠雄株增加异交花粉的数量和质量,避免自交衰退;同时两性花的自交亲和保障生殖成功.流苏树雄花的雌蕊退化,从另一个角度证明木犀科的雄全异株是两性株向雌雄异株进化的过渡状态.%Androdioecy is a rare reproductive strategy in plants.Comprehensive studies on the flowering dynamics,pollinators,morphology,and structure of flowers,breeding systems,and controlled pollination were performed in four populations of the Chinese fringe tree,Chionanthus retusus.This species is typically androdioecious in morphology,with male and hermaphroditic individuals coexisting in the same population.Results showed that the development of the stamens of male and hermaphrodite flowers was similar,and could produce functional 2-cell pollen grains.Two carpel primordia appeared inside the stamens of males and hermaphrodites at the initial pistil stage.Subsequently,these two carpels fused with each other and differentiated into the ovary and stigma in hermaphroditic flowers.However,in males,a cavity was formed after the fusion of two carpels,and it stopped growing further and eventually degenerated.This species was protogynous,and the stigma was receptive throughout anthesis.Pollen grains were viable after anther dehiscence and the viability was maintained at ＞ 10％ for about 2 weeks at room temperature of 20-25°C.C.retusus is a wind-and insect-pollinated species,and the main pollinating insects belonged to Thripidae and Syrphidae.The results of controlled experiments 30 days after pollination showed that C.retusus could bear fruit under natural conditions with fruit set percentage of 34.36％.The hermaphroditic flowers were self-compatible,and the fruit set percentage under autogamy was very low,i.e.,only 10.70％.No apomixis was observed.In artificial pollination,the fruit set percentage with cross-pollination (xenogamy with pollen from male or hermaphroditic flower) was significantly higher than that with self-pollination (geitonogamy) (P ＜ 0.05).Sexual reproduction of this species was limited by the pollinators.It was demonstrated that C.retusus presented a mixed mating system,because it can produce fruit under any type of pollination tested.In terms of functional gamete production from both males and hermaphrodites,C.retusus represents a novel case of functional androdioecy in the family Oleaceae.The maintenance mechanism of androdioecy of this species could be as follows:males increase the quantity and quality of pollen,which can avoid inbreeding depression,and the self-compatibility of hermaphrodites might ensure reproductive success.Based on the presence of pistillodes in male flowers,and the results of previous studies,androdioecy might be a transition from hermaphroditism to dioecy in Oleaceae.
