Synchronous flowering times and asymmetrical hybridization in Typha latifolia and T. angustifolia in northeastern North America

Cattails (Typha spp.) in northeastern North American wetlands are increasingly dominant, partly because of hybridization between Typha latifolia and Typha angustifolia which results in the widespread and successful hybrid T. × glauca. Both parental species are protogynous, and previous studies have shown that T. angustifolia flowers earlier than T. latifolia. Nevertheless, experimental studies have shown that hybridization is overwhelmingly asymmetric, involving T. angustifolia female flowers and T. latifolia pollen which should have minimal overlap in the times at which they are produced. In this study we surveyed two Typha stands in eastern North America, and at both sites found substantial overlap in the times at which the parental species and the hybrids shed pollen and presumably are receptive to fertilization; this means that flowering time is not a prezygotic barrier to either the formation of hybrids or their subsequent backcrossing to parental species. Consistent with experimental studies, all hybrids had T. angustifolia as their maternal parent. Our results suggest that reproductive barriers between Typha spp. are evolving.

► The cattails Typha latifolia and T. angustifolia hybridize in eastern Canada. ► All hybrids had a T. angustifolia female parent and a T. latifolia male parent. ► Flowering times of the parental species overlapped considerably more than expected. ► Changing reproductive barriers may be influencing the frequencies of hybrids.