Sex Expression of Gurania and Psiguria (Cucurbitaceae): Neotropical Vines that Change Sex

Gurania and Psiguria, long thought to be dioecious, are actually monoecious; values of Gp, a quantitative measure of an individual's phenotypic gender, are bimodally distributed in natural populations. Individual vines undergo two kinds of sex change: size-related and intraseasonal. Small (in diameter) plants produce only male flowers; only large plants produce female flowers. In favorable greenhouse situations, plants that reach large sizes switch from all male to female flowering; in poor conditions, the same genotypes remain vegetative or male, or switch back from female condition. Intraseasonal sex change occurs when plants initiate a predominantly female flowering episode with a few functional male inflorescences. Such protandrous vines are usually unisexual any point in time. Since neither type of sex change is obvious without long-term observations, we suggest that other “dioecious” angiosperms should be more carefully studied.