XVI International Botanical Congess

Seventy-three genera of Rubiaceae, with approximately 700 species have been recorded from the tropical Andes above 1000 m altitude. Only two genera (2.9%) but ca. 430 species (61%) are endemic to this area. This seems to imply a relatively recent diversification of the flora, in accordance with the relatively recent origin of Andean habitats. Three different scenarios may be imagined for the evolutionary origin of the Andean flora: (1) it may have evolved from ancient lowland ancestors in response to uplift of the mountains, (2) its ancestors may have reached the area by immigration from adjacent temperate South America into the newly-formed habitats, and (3) its ancestors may have reached the newly-formed habitats by long distance dispersal. Each of these hypothetical scenarios imply differences concerning distribution of sister groups and relationships between low altitude and high altitude taxa. Phylogenetic reconstructions for several groups of Andean-centered Rubiaceae suggest examples of all three scenarios. The dominant pattern is diversification from pre-existing lowland lineages and this is exemplified by the tribes Cinchoneae and Psychotrieae. Immigration from the south seems to have played a minor role, the only example may be in the tribe Anthospermeae. Also long distance dispersal seems to have been rare: the genus Arcytophyllum is the only example identified so far.