Solanum marginatum is andromonoecious, with long-styled hermaphrodite flowers and medium- or shortstyled female sterile flowers which produce fertile pollen. The morphology of the three floral types is compared. The female sterile type is determined prior to the stage at which the flower buds are visible. In this type, development of most ovules was arrested at the megasporocyte stage. Self-compatibility and a large number of flowers simultaneously open on a plant suggest that, in S. marginatum, andromonoecy does not promote outbreeding. We propose that the functionally male flowers aid in attracting and sustaining pollinators and ensure high rates of fertilization through an increased pollen/ovule ratio. Possible effects of andromonoecy on seed dispersal biology are discussed.