Geitonogamy: The neglected side of selfing.

Flowers of many angiosperm species are well adapted to avoid self-pollination, for instance by temporal and spatial separation of pollen and stigma within the same flower. However, such adaptations do not prevent the transfer of pollen between flowers on the same plant (geitonogamy). Recent empirical studies, aided by advances in field techniques, statistical methods and modelling, show that geitonogamy often is substantial and increases with plant size. Selfing by geitonogamy incurs a fitness cost of reduced pollen export, and recent reports show that seed set can suffer as well, even in self-incompatible species. Geitonogamy has important implications for sex-allocation theory, the evolution of dioecy and other issues in evolutionary biology.