Cleistogamous capitulum in Centaurea melitensis (Asteraceae): Heterochronic origin

Cleistogamous capitula formed by Centaurea melitensis display a number of m orphological and functional changes with respect to chasmogamous capitula t hat ensure self-fertilization. Because no studies have hitherto addressed t he evolution of cleistogamy in Asteraceae, it was considered useful to asce rtain whether these changes are attributable to one or more of the heteroch ronic processes reported in the literature. Bivariate allometric analyses w ere performed, and changes were represented graphically using Gould's clock models for size, shape, and age of several capitulum and floret structures . Results suggest that the partially paedomorphic appearance of cleistogamo us with respect to chasmogamous capitula is attributable to three processes : (1) early onset of floral development (predisplacement), (2) decreased gr owth rate of the whorls studied (except gynoecium width) and (3) early offs et time (progenesis). The latter appears to play the most significant role in the origin of the cleistogamous capitulum.