Résumé
Crepis sancta is an annual composite that colonizes abandoned agricultural land and shows achene dimorphism. The achenes on the periphery of the capitulum are heavy (0.27 mg) and are without a pappus, whereas those in the center are light (0.10 mg), more numerous, and bear a pappus. Several studies of other species of Asteraceae have shown that these morphological differentiations are accompanied by biological differences, but few studies have tested whether these differences are constant between populations. We compared the germination, growth, phenology, and reproductive effort of plants derived from these two types of achenes from three populations that had been established for 3, 13, and 36 yr. The peripheral achenes from the young population germinated fastest and gave rise to the most vigorous individuals. The differences in the two other populations were slight or nonexistent. By comparing the morphs between populations, pregermination dormancy and plant vigor were found to be different among populations for the central achenes, whereas the characteristics of the peripheral achenes remained almost unchanged. It is often hypothesized that achene dimorphism is due to developmental constraints. Our results indicate that these constraints may be regulated by environmental conditions.