An angiosperm-wide analysis of the correlates of gynodioecy

Premise of research. Gynodioecy, a dimorphic sexual system where individual plants are either female or hermaphroditic, has been documented in ≪1% of plant species. This rarity suggests that gynodioecy can evolve and persist only under a restrictive set of conditions. One approach to determining these conditions is to identify the phenotypic traits and ecological factors that are associated with gynodioecy, as such traits or factors may facilitate the evolution and persistence of the sexual system. Methodology. We assembled an angiosperm-wide database of gynodioecious species and used this database to test whether gynodioecy was associated with two phenotypic traits/ecological factors: an herbaceous growth form and a temperate geographic distribution. Species-level analyses were used to confirm that gynodioecious species are predominately herbaceous and temperate. Family-level analyses were then used to test whether the presence of herbaceous and temperate species in a lineage was associated with the presence of gynodioecious species. Pivotal results. An herbaceous growth form and a temperate geographic distribution were significantly overrepresented in gynodioecious species relative to their frequency in all plant species. Families that contained species with an herbaceous growth form and a temperate geographic distribution were significantly more likely to also contain gynodioecious species. Conclusions. Gynodioecy was associated with an herbaceous growth form and a temperate distribution, suggesting that herbaceousness and temperateness can facilitate the evolution and/or persistence of gynodioecy. In addition, our results suggest that gynodioecy is associated with different phenotypic traits/ecological factors than dioecy, a closely related sexual system. Consequently, whether gynodioecy is a transitional state in the evolution of dioecy may depend on the growth form and geographic distribution of the lineage in which it evolves.