Reproductive biology of duodichogamous Koelreuteria elegans (Sapindaceae): the rare case of a female–male–female flowering sequence

Abstract

Monoecious species are common within Sapindaceae, and among them a large variation in sexual expression has been reported. In this work we evaluate the sexual expression, phenology, floral biology, and mating system in eight to sixteen individuals of the duodichogamous Koelreuteria elegans (Seem.) A.C. Sm. subsp. formosana (Hayata) F.G. Mey. Results from our study show that all individuals exhibited a pattern of flowering characterised by two cycles of pistillate flowers with an intervening one of staminate flowers. The synflorescences presented a high synchronisation between the male and female phases at the individual level. Therefore, very little functional overlap was observed between pollen receipt and pollen dispatch within individuals. Pollination was by bees, and the manual pollination experiments showed that this species is a xenogamous although self-compatible species. Nevertheless, seed set increased significantly with hand cross-pollination and open pollination experiments. Decrease of fruits and seeds set by geitonogamy could favour the establishment of duodichogamy with interfloral protogyny promoting cross-pollination. In the family this is the first report of a pattern of flowering in which there are two cycles of female with an intervening cycle of male flowers. The importance of detailed these studies for understanding mechanisms underlying duodichogamy was demonstrated, and findings will help to broaden our understanding about this rare sexual system to generalise the specific ecological factors that explain its evolutionary meaning.