Self‐compatible (SC) plants often deposit pollen on their own stigmas before flowers open. Thus, if we find natural hybrids between a SC species and a closely related self‐incompatible (SI) species, the pollen donor is usually expected to be the SC species. However, in previous studies of naturally occurring mixed populations of invasive Cakile maritima (SI) and Cakile edentula (SC) in Australia, hybridisation was found to have been bidirectional. Here, we explored the floral development of these species in order to test the hypothesis that there might be a short opportunity for pollinators to visit open SC flowers before the self‐pollen is released. Results indicated that both species showed reverse herkogamy during early development, though by the time pollen was ripe the four long anthers always overtopped the stigma; in C. maritima, most of the short anthers remained below the stigma. In both species, ripe, compatible pollen was able to germinate on the stigmatic surface at all stages of floral development. Anther dehiscence commenced earlier in C. edentula and well before flowers opened, in contrast to C. maritima, but the timing of pollen release varied between individual flowers, with a small proportion of uncontaminated stigmas after flowering; therefore, C. edentula can be either pollen recipient or pollen donor when interspecific outcrossing occurs. In summary, our results suggest that the variation between individual flowers of C. edentula contributed to the bidirectional hybridisation despite being a predominant selfer, providing new insights into plant colonisation.

中文翻译：

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自相容物种和自相容物种之间的自然杂交如何是双向的？

自相容（SC）植物通常在花开前在其柱头上沉积花粉。因此，如果我们发现SC物种与密切相关的自我不相容（SI）物种之间存在天然杂种，则通常可以认为花粉供体是SC物种。但是，在以前的自然研究中，侵袭性地中海沿岸小岛礁（Cakile maritima，SI）和地中海小岛蓝藻（SC）在澳大利亚，发现杂交是双向的。在这里，我们探索了这些物种的花期发育，以检验以下假设：传粉者在释放自花粉之前可能有短暂的机会访问开放的SC花。结果表明，尽管到花粉成熟时，四个长花药总会超过柱头，但两个物种在早期发育过程中均显示出逆向同源性。在滨海假丝酵母中，大多数短花药保持在柱头以下。在这两个物种中，成熟的，相容的花粉在花发育的所有阶段都能够在有斑点的表面发芽。与海蓝藻相反，花药开裂最早发生在小叶海棠和开花之前。a，但花粉释放的时间因各花而异，开花后未受污染的柱头的比例很小；因此，发生种间异交时，小肠弯曲杆菌既可以是花粉接受者，也可以是花粉供体。总而言之，我们的结果表明，尽管主要是自交者，但蓝靛果单个花之间的变异还是促进了双向杂交，为植物定植提供了新的见识。