Plant Diversity of the Cape Region of Southern Africa

Abstract

Comprising a land area of ca. 90,000 km2, less than one twentieth (5%) the land area of the southern African subcontinent, the Cape Floristic Region (CFR) is, for its size, one of the world’s richest areas of plant species diversity. A new synoptic flora for the Region has made possible an accurate reassessment of the flora, which has an estimated 9030 vascular plant species (68.7 % endemic), of which 8920 species are flowering plants (69.5 % endemic). The number of species packed into so small an area is remarkable for the temperate zone and compares favorably with species richness for areas of similar size in the wet tropics. The Cape region consists of a mosaic of sandstone and shale substrata with local areas of limestone. It has a highly dissected, rugged topography, and a diversity of climates with rainfall mostly falling in the winter months and varying from 2000 mm locally to less than 100 mm. Ecological gradients are steep as a result of abrupt differences in soil, altitude, aspect, and precipitation. These factors combine to form an unusually large number of local habitats for plants. Sandstone-derived soils have characteristically low nutrient status, and many plants present on such soils have low seed dispersal capabilities, a factor promoting localized distributions. An unusual family composition includes Iridaceae, Aizoaceae, Ericaceae, Scrophulariaceae, Proteaceae, Restionaceae, Rutaceae, and Orchidaceae among the 10 largest families in the flora, following Asteraceae and Fabaceae, as the most speciose families. Disproportionate radiation has resulted in over 59.2 % species falling in the 10 largest families and