The Cape Region contains arguably the most unique and diverse flora of any temperate area of the world. Its status as a distinct floral kingdom is reinforced by the presence of five endemic families—Geissolomataceae, Grubbiaceae, Penaeaceae, Roridulaceae, and Stilbaceae. Moreover, 193 endemic genera comprise 19.5 percent of the total.
Covering an area of only 78,500 square kilometers, the Cape Region contains about 9,000 species of vascular plants. The ten largest genera of the Cape Region account for over 20 percent of the flora, led by Erica (Ericaceae, 658 species) and Aspalathus (Fabaceae, 257 species). Other large genera are Phylica (Rhamnaceae), Agathosma (Rutaceae), Oxalis (Oxalidaceae), Pelargonium (Geraniaceae), Senecio (Asteraceae), Cliffortia (Rosaceae), Muraltia (Polygonaceae), and Ruschia (Aizoaceae-Mesembryanthema).
Levels of species endemism in the Cape floristic region are among the highest in the world. For the entire region, endemism at the species level is about 69 percent. The high levels of endemism present in the Cape Region are largely due to the presence of neoendemics rather than paleoendemic species. This dominance of neoendemics is indicated by the predominance of endemic diversity in large, species-rich genera, the widespread presence of sympatric congeners, and the edaphic specialization of many endemics on geologically young substrates. Rather than being a random ecological or phylogenetic assemblage of species, the great majority of endemics are low shrubs killed by fire and dependent on closely dispersed seeds for regeneration.
Four families are notably rich in endemics—the Proteaceae, Ericaceae, Rutaceae, and Polygalaceae. Species richness is greatest in the southwestern Cape Region centered around Cape Town. The Cape Peninsula, for example, supports 2,256 species (including 90 endemics) in an area of 471 square kilometers. Cape Hangklip on the eastern shore of False Bay near Cape Town has 1,383 species in 240 square kilometers.
Smaller regional centers of high endemism exist within the Cape Region. Dividing the Cape Region into five floristic zones on the basis of species distributions within seven large families, regional levels of endemism are highest in the southwestern and northwestern Cape (about 50 percent) and lowest in the eastern Cape and Inland Mountain regions with nonseasonal rainfall (18–28 percent). These patterns of regional endemism have been further demonstrated in studies of distribution of the Proteaceae in the Cape Region. For the entire Cape Region, 99.4 percent of the 330 species of Proteaceae are endemic. At a regional level, 63 percent of the Proteaceae in the southwestern region are endemic to that region, compared with only 19 percent for the Coastal Mountain and Southeastern Regions. Point endemism is also widespread involving species that are restricted to highly specific edaphic habitats.
Fynbos plant diversity is also extremely high at the alpha-diversity level of small stands. Typical fynbos communities support a mean of about 65 vascular plant species in 0.1 ha, with a range of 31–126 species reported. Renosterveld shrublands have even higher diversities with a mean of 84 species per 0.1 ha and a range of 28–143 species.