The avoidance of interference between the presentation of pollen and stigmas in angiosperms I. Dichogamy

Abstract Dichogamy is the separation of the presentation of pollen and stigmas in time within a plant. It is a common but neglected feature of outcrossing angiosperms. Dichogamy has been almost universally interpreted as an outcrossing mechanism, but many dichogamous species are also self-incompatible (and sometimes also herkogamous and/or with unisexual flowers). In outcrossing species, there is almost invariably a clash between selection to place pollen and stigmas in similar positions for effective pollination and selection to keep the androecia and gynoecia apart to avoid interference between them. We suggest that the separation of pollen and stigmas acts in general to reduce this self-interference and it often also reduces self-fertilisation. Mechanisms preventing self-fertilisation primarily increase maternal fitness, whereas mechanisms avoiding self-interference primarily promote paternal fitness. Five independent ways of subdividing dichogamy are recognised: protandry or protogyny; intrafloral or ...