Radiation of the Hypochaeris apargioides complex (Asteraceae: Cichorieae) of southern South America

Abstract

Radiation into different environments is a common evolutionary phenomenon in plants. This process has been extensively documented in oceanic islands and to a lesser extent in continental areas. The genus Hypochaeris (Asteraceae: Cichorieae) contains 41 species in South America that have evolved during the past one million years. Dispersal of propagules to new regions followed by speciation at the diploid level into different ecological zones has resulted in radiated groups. One such group, the H. apargioides complex, consists of four closely related species, H. apargioides, H. gayana, H. spathulata, and H. thrincioides, all of which are distributed in central-south Chile and adjacent Argentina. Morphometric and molecular (AFLP) data were used to help reveal processes involved in the evolution of the complex. A total of 54 populations were sampled: 34 were analyzed morphometrically and 45 were examined for genetic variation and divergence using AFLP methodology. Morphometric analysis shows that two species, H. gayana and H. spathulata, are clearly separated phenotypically from the others, but that H. apargioides and H. thrincioides are more similar to each other. The principal environmental conditions influencing morphology and distribution of species in the H. apargioides complex appear to be salinity and elevation in H. spathulata and H. gayana, respectively, and climate in H. apargioides and H. thrincioides. The overall pattern in the evolution of the complex is one of subtle morphological divergence in response to environmental selection, perhaps reflecting initial stages of adaptive radiation. The low level of molecular divergence among species also suggests rapid speciation.