The allometry of flower size dimorphism in dioecious Dombeya species on LaReunion

In this paper we examine whether variation in male and female flower size f ollows an allometric relation for 10 dioecious species in the genus Dombeya endemic to La Reunion. Male flowers are significantly larger than female f lowers and the degree of dimorphism varies significantly across species. Th ere is a significant allometric relationship between male and female flower size: as mean flower size decreases the degree of flower size dimorphism i ncreases. This is the first study to document an allometric relationship be tween male and female flower size in unisexual plants. We discuss this allo metric relationship in relation to two characteristics frequently observed in dioecious flowers: flower size dimorphism is common in unisexual plants and dioecious species often have smaller flowers than hermaphrodites.