Dioecy and Monoecy in the Flora of Puerto Rico and the Virgin Islands: Ecological Correlates

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Abstract
The frequency of dioecy and monoecy and the ecological correlates of each sexual system were examined for the flora of Puerto Rico and the Virgin Islands. Of the 2037 spp. in the total flora, 6.1% are dioecious, 10.5% are monoiecious, 2.4% are andromonoecious, 2.0% are gynomonoecious and 78.9% are hermaphrodites. To test the null hypotheses that there is no relationship between sexual system and endemism, growth habit or fruit type, the proportionate distribution of dioecious and monoecious taxa (genera and/or species) in each of these categories was compared to that for the entire flora, or for trees and shrubs. Endemics are not disproportionately represented among dioecious or monoecious species. There is no association between monoecy and growth habit, either for genera or species, but dioecy is significantly more common than expected in trees, and less common in herbs, at both generic and species levels. For the entire flora, dioecious genera and species are significantly associated with fleshy fruits, but monoecious taxa are not. For trees and shrubs, dioecious species are significantly associated with fleshy fruits, while monoecious species are significantly associated with dry fruits. On the generic level, there is no association between fruit type and sexual system for trees and shrubs. Dioecious trees and shrubs contain more genera and species with 1-seeded, fleshy fruits and fewer genera and species with many-seeded, fleshy fruits than expected. Monoecious trees and shrubs contain fewer genera and species with many-seeded, fleshy fruits and more genera and species with many-seeded, dry fruits than expected. These data are discussed in the context of several theories concerning the evolution of plant sexual systems.

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