Southern Africa, including Namibia (South West Africa), South Africa, Lesotho, Swaziland, and Botswana, covers an area of ca. 2.5 million km2. The flora comprises ca. 18,500 species in 1,930 genera. There are 10 endemic families, while 80% of the species and 29% of the genera are endemic. Of the five phytogeographic regions recognized, the Cape Floristic Region is the richest and most distinctive, and in this small area there are some 8,550 species in 957 genera. Most of the subcontinent is arid to semiarid. Its rich and diverse flora, contrasting with the relatively depauperate tropical African flora, is believed to have evolved gradually since the early to mid-Tertiary at the southern edge of the tropics as Africa became progressively drier, partly from an ancient southern African temperate flora and partly from a tropical African forest flora. The large number of species in the Cape Region and adjacent arid areas probably evolved recently in the last 1-2 million years as the climate fluctuated violently during the Pleistocene. Peculiarities of the flora include an unusually high proportion of petaloid monocots, a wealth of succulents, mainly in winter rainfall arid areas, large numbers of sclerophyllous to microphyllous shrubs, and very few annuals.