Consequences of Pollination Syndrome Evolution for Postpollination Biology in an Ancient Angiosperm Family

Abstract

Evolutionary shifts from insect to wind pollination involve a host of modifications to floral structure and phenology, but little is known about how floral modifications that facilitate pollination might affect the fertilization process. Within the water lily family Cabombaceae, there is evidence that wind pollination arose recently in Brasenia, whereas the sister genus Cabomba became specialized for fly pollination. Both species have an apomorphic stylar extension, which in Brasenia became greatly elongated to produce a much larger stigmatic surface. Consequently, pollen tubes in Brasenia must travel much farther to reach ovules, and because mean pollen tube growth rates are similar (750–950 μm/h), fertilization occurs ∼4 h later in Brasenia than in Cabomba. In both genera, pollen tubes grow between cells of the substigmatic ground tissue and then within an open, secretion‐filled stylar canal and ovarian cavity. In Brasenia, early pollen tube development is slower than in Cabomba, which may be a result o...