The historical phytogeography of the Disinae (Orchidaceae)

Abstract

The Disinae (Orchidaceae) are widespread in tropical montane Africa and the Cape temperate region, therefore showing a distribution range typical of a temperate herb in Africa. Centres of endemism and high species richness are recognized in the southern and western Cape Province, the Natal-Transvaal escarpment mountains, the watershed between the Rivers Zaire and Zambesi and the southern highlands of Tanzania, the East African highlands and Madagascar. The number of species and their degree of endemism decrease from south to north. Several regions, e.g. Zimbabwe and West Africa, are outliers of other regions, or overlap zones between regions. An attempt is made to determine the history of the group by vicariance biogeographical analysis, but the resultant area cladogram is uninformative. This may be due to the vagility of the taxa.Areas of endemism of supra-specific taxa are determined. These areas appear on recent palaeoenvironmental data to be possible refugia (Cape fold mountains, the South African Drakensberg and the East African Rift Valley mountains), from where the taxa spread when the climate ameliorated after the last glacial. This model is corroborated by recent studies on Cupressaceae, Pooidae and Compositae.