Historical biogeography of Androcymbium Willd. (Colchicaceae) in Africa: evidence from cpDNA RFLPs

The cpDNA restriction variation in 39 populations representing a geographic al sampling of IS species of Androcymbium in southwestern and northern Afri ca was examined to assess the historical biogeography of the genus. The cpD NA phylogeny indicates that the disjunction between South and North Africa is best explained by the dispersal of southern African ancestors into North Africa. Divergence time estimates suggest that the geographic range of the genus may have extended considerably north (perhaps to Tanzania and Kenya) prior to the global desiccation of Africa in the Miocene. Further expansio n of the genus northward was probably stalled until climatic changes in the late Miocene brought about the gradual replacement of a subtropical woodla nd savanna with the and landscape that gave rise to the Sahara. Aridificati on of the northern quarter of the continent provided the ecological conditi ons for fostering the expansion of Androcymbium along the Mediterranean fri nge (probably east to west) and its introduction into the Canary Islands. U nlike their South African congeners, the northern species have experienced expansions, fragmentations, and local extinctions in response to the severe climatic shifts in this area during the Pliocene-Pleistocene. According to our divergence time estimates, the and track may have already existed as a continuous area connecting southern and northern Africa in the late Miocen e. (C) 2001 The Linnean Society of London.