INCIDENCE OF MONOECY AND DICHOGAMY IN RELATION TO SELF-FERTILIZATION IN ANGIOSPERMS

The evolution of many floral traits, including monoecy and dichogamy, has been attributed to selection for avoidance of self-fertilization. If this explanation is correct, monoecy and dichogamy should be uncommon among self-incompatible species because physiological barriers prevent self-fertilization in such species. In fact, self-fertility was independent of sexual system in a sample of 588 hermaphroditic and monoecious angiosperms. Overall, dichogamy was also equally common among self-incompatible and self-compatible species. When the different forms of dichogamy were analyzed separately, only intrafloral protogyny was associated with self-compatibility. This form of dichogamy is less common among angiosperms than intrafloral protandry, which is probably less effective at reducing self-fertilization. Thus, avoidance of self-fertilization has probably been less important in the evolution of monoecy and most forms of dichogamy than other factors, such as avoidance of pollen-pistil interference, and flexibility of resource allocation to male and female functions.