Sexual expression and reproductive output in the ephemeral Geranium transversale are correlated with environmental...

Abiotic environmental factors are often considered to be important in the distribution and maintenance of variation in sexual systems in flowering plants. Associations between sexes and abiotic factors are well documented in dioecious systems, but much less is known about this relationship in other sexually polymorphic systems. Species that are highly variable in sexual expression and habitat distribution can provide insights into the role of abiotic factors in maintaining variation in sexual expression.

Focusing on a sexually polymorphic species, Geranium transversale, we measured sexual expression at both the flower and the plant level and examined vegetative and floral traits, pollen deposition, and reproductive success. We also tested for correlations between sexual expression and other traits and examined whether and how these traits covaried with abiotic environmental conditions.

We identified unique variation of sexual expression in G. transversale. There are four sexual morphs that display different combinations of the three flower types (pistillate, staminate, and perfect). Sexual morphs that are phenotypically more female (i.e., female and gynomonoecious morphs) are found in wetter and milder environments, and flower earlier than morphs that are more male (i.e., hermaphroditic and andromonoecious morphs). Additionally, floral organ size and reproductive success are influenced not only by the flower type but also by the sexual morph of the plant.

Environmental conditions are likely to cause some of the variation in sexual expression found in G. transversale. Both genetic and ecological factors likely contribute to the maintenance of sexual variation in this species.