Abstract: During the evolution of plant mating systems, the generally accepted mechanism for the evolution from hermaphroditism to dioecy is for the existence of an intermediate gynodioecious step.  Since many more plants are gynodioecious than dioecious, it is possible that gynodioecy may itself be evolutionary stable.   The implication of this is that selection must occur to maintain hermaphrodite individuals in this population.  If the gynodioecious species exists as a metapopulation, selection may also favor selfing hermaphrodites as colonists and allow the system to maintain itself.  This study examined the abilities of hermaphrodites and females in a weedy gynodioecious species, S. vulgaris (Caryophyllaceae) to successfully colonize new areas and examine if this may be a selective pressure maintaining gynodioecy.  While females proved to be more fit in experimental established populations, hermaphrodites were far more fit in isolated, pollen-limited environments.  These results may indicate that hermaphrodites are better able to colonize new habitats.  These results further suggest that selection for the superior colonizing ability of hermaphrodites may explain the evolutionary stability of gynodioecy, at least in species which exist as metapopulations.