XVI International Botanical Congess

The phylogeny and biogeography of Helianthinae were studied using morphology, ITS sequences, and chloroplast DNA restriction sites. An origin in Mexico is suggested based on the composition of basally diverging clades. Secondary radiations in South America and North America appear to be recent, based on low levels of molecular divergence. A recurrent pattern of molecular variation is the presence of a well defined branch leading to a cluster of species which exhibit little divergence. This suggests that there have been several rounds of radiation in the subtribe, and that the extant array of species in some lineages may be of relatively recent derivation. The presence of groups of species with a common syndrome of morphological characters interspersed with phenetically distinct groups throughout the subtribe makes generic level delimitation a challenge.