CONICET | Buscador de Institutos y Recursos Humanos

?Gynodioecy?dioecy? is one of the pathways bywhich dioecy can arise from hermaphroditism. Studies onsex determination and development of gynodioecious systemshave focused on temperate and/or annual species.Little is known about the evolutionary dynamics of gynodioecyand dioecy in perennial tropical species, where thesesystems have more frequently evolved. Maytenus obtusifoliais an abundant species in restingas in southeasternBrazil. The sexual system of M. obtusifolia was investigatedby studying the floral structure and reproductivebiology. We considered the sexual system as an intermediatestep in the pathway gynodioecy-dioecy. The characterizationof the hermaphrodite morph was complex,because of a gradient of variation in floral morphology andreproductive characteristics (sizes of the style and stigmaticsurface, pollen viability, embryo sacs containing hypertrophiedsynergids, and fruit set). This variation leads todifferent proportions of functional male and female flowersamong hermaphrodite plants and is responsible for thedifferent levels of reproductive success. Female reproductivesuccess and pollen viability were negatively correlatedwith the hermaphrodite morph (r = -0.67). The higherfruiting intensity and fruit/flower ratio of females (41 %)compared to hermaphrodites (2 %) and the fact that femaleplants produce more and better-quality seeds support thefemale compensation. We suggest that female sterility maybe linked to the set of changes in the carpels. The differencesin the quality and quantity of pollen grains of hermaphroditeplants, and the similar individual rates of pollenviability observed for three consecutive flowering events,may indicate a relationship with nuclear cytoplasmic sexdetermination.