To be successful as a colonizer, a plant must be capable
of increasing its numbers at low densities. A plant capable
of vegetative reproduction may have a selective advantage
over a plant that only reproduces sexually because even a
single individual would be able to reproduce and colonize
new habitats (Baker 1962, 1965). If a plant is incapable of
vegetative reproduction and only reproduces sexually
through cross-pollination (allogamy), then having both
sexes on the same plant [i.e., either a monoecious plant or
a plant with perfect flowers (hermaphrodite)] may confer a
selective advantage over a unisexual (dioecious) plant.
Any two plants would be capable of reproduction and
colonization (Baker 1962). If a plant is bisexual, then selfcompatibility
may confer a selective advantage over selfincompatibility
because just a single plant is capable of
reproduction and colonization (Baker 1962, 1965).