THE HETEROCHRONIC ORIGIN OF THE CLEISTOGAMOUS FLOWER IN ASTRAGALUS-CYMBICARPOS (FABACEAE)

Members of the species Astragalus cymbicarpos form chasmogamous and cl eistogamous flowers, as well as a large variety of intermediate floral types. Bivariate allometry and Gould's clock models were used to inve stigate the possible heterochronic evolution of the cleistogamous flow er from the chasmogamous flower. In three of the whorls analyzed (pist il, stamens, and corolla) comparison of chasmogamous, pseudocleistogam ous, and cleistogamous flowers revealed a progressive ''juvenilization '' of the adult form. This paedomorphic morphology proved to be partly the result of a process of progenesis, also evident in acceleration o f sexual maturity. The retardation of shape with respect to size in th ese three whorls suggests, however, the existence of a heterochronic p rocess other than progenesis.