Deserts in South Africa are confined to the northernmost part of the west coast, in the narrow corridor along the Orange River. Despite the hyper-arid nature of the region, plant species richness of the desert units is very high when compared with other deserts at the same level of aridity globally. Especially in the Richtersveld, diversity is remarkably high and does not differ much from that in the Succulent Karoo part of the Richtersveld. Annual rainfall is usually much lower than 80 mm.