XVI International Botanical Congess
Macaronesian Crassulaceae include 70 species (65 endemic) and 6 genera. Molecular phylogenetic analyses indicate that this group resulted from six colonizations: one for Crassula and Umbilicus, three for Sedum, and one herbaceous, Sedum-like colonist for the Sempervivoideae (Aeonium, Aichryson, Monanthes. In Sempervivoideae, speciation and adaptive radiation resulted in a great diversity of growth-forms, adaptation to dryer habitats and lignification were general trends. Radiation in Sedum ser. Macaronesia followed a similar pattern, woody forms adapted to dry cliffs evolved from a herbaceous immigrant. Macaronesian Sedum are sister to ca. 250 Crassulaceae of Mexico and South America. The enormous growth-form variation within this latter group offers a unique challenge for studies of adaptive radiation in a continental setting.