Abstract

Flowering-time, plant longevity and size of capitulum were studied in a common garden experiment on seven populations of annual Chaetanthera moenchioides derived from a strong latitudinal aridity gradient in the mediterranean climate area of Chile. Populations derived from the drier northern part of the latitudinal gradient showed significantly shorter flowering and fruiting phenology and smaller capitula under uniform growing conditions. Water stress experiments performed in the greenhouse induced further phenological hastening and a reduction in number of ray florets per capitulum. Population differentiation and the reaction norms in C. moenchioides agree with the predictions of genetic-assimilation given that the plastic response of the species under water stress mimics phenotypic differentiation that has evolved along the environmental gradient. © 2009 Springer-Verlag.