The rust mycobiota of southern Africa: species richness, composition, and affinities.

The rust mycobiota (Uredinales, Basidiomycota) of southern Africa (Botswana, Namibia, and South Africa) is analysed with regard to species richness, generic composition, and similarities to the rust mycobiotas of the remaining African continent and other regions of the world. Southern Africa is home to about 546 rust species: ca 522 species have been reported from South Africa, 73 from Namibia, and less than ten from Botswana. Thirty-two species were considered to be exotics. Two hundred and twenty-five of the species are restricted to southern Africa, suggesting an endemism rate of ca 44%. At present, the rust fungus:host ratio is 1:38.5, which is much lower than expected from other regions of the world. This low ratio may partly be due to under-exploration of the area, but the results presented here indicate that a natural paucity of rust fungi on certain, especially species-rich plant taxa centred in southern Africa and possibly environmental factors are more important reasons. The predominant genera are Puccinia and Uromyces accounting for ca 59% of the rust species. The genera Hemileia, Phakopsora and especially Ravenelia, centred in tropical regions, are well represented and sum up to 8% of the species. Members of Melampsoraceae and Phragmidiaceae, common in temperate regions of the Northern Hemisphere, are scarce. Most of the other 28 recorded teleomorph genera are only represented by three or less species. In an African context, most species are shared with central and east Africa (almost 16%). Only a few species are disjunct between southern and West Africa or Madagascar. Ca 10% of the species are shared only with other parts of the paleotropics, especially the Indian subcontinent. Disjunctions of native species with the New World, Australia/New Zealand, or Europe are rare.