Open AccessThe genus Mariscus occurs over practically the whole of the Flora of Southern Africa (FSA) region, with the exception of the west coast and the Karoo region of the Cape Province. Practically no species occur under conditions of less than 250 mm of rain per annum, whereas the highest concentrations of subgenera/sections and species occur where the annual rainfall is more than 500 mm. All the species in the region are summer rainfall plants, or if they occur in the winter rainfall area they behave like summer rainfall plants. The different subgenera/sections recognized within the genus differ widely in respect of their water requirements, yet there is a general concentration of taxa in the eastern part of the country where the rainfall is higher than in the west. Nevertheless, the highest concentrations of taxa are not in the areas of highest rainfall, which suggests that topographical diversity is probably the most important factor determining concentrations of taxa.
The geographical distribution of each subgenus/section in the FSA region is explained in relation to the total distribution of the subgenus/section. The possible climatic or environmental conditions which may determine the distribution of each subgenus/section are mentioned, and the concentration of species within each subgenus/section is demonstrated by means of maps.