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 G p , 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.