The desert of South Africa is a part of the hyperarid region fringing the western South Atlantic seaboard, southern Angola (Mossamedes Desert) and Namibia (Namib Desert). The great age of aridity (presumably dating back to Late Miocene), extraordinary high diversity of organisms (including many endemics), a wide spectrum of adaptations to arid environments and the inclusion of both winter- and summer-rainfall areas make these desert areas one of the most interesting hyperarid regions in the world. Within South Africa, the desert areas stretch from the Atlantic coast near the mouth of the Orange River and penetrate inland following the course of the lower Orange River as far as the vicinity of Onseepkans and Pofadder in northern Bushmanland. In the eastern part, most of the desert area within South Africa lies within less than 20 km from the Orange River and only very few parts are further than 30 km away from the river. This is mirrored on most of the Namibian side of the river, revealing a relationship between the low elevation of the land surface next to the Orange River and the formation of hyperarid desert conditions. West of 17° longitude the Namibian part of the Namib Desert is no longer limited to the larger Orange River Valley - the desert extends northwards over the whole coastal plain (with some interspersed enclaves of Succulent Karoo in the southwest) throughout Namibia into the southwestern corner of Angola. It must be emphasised that this broad desert area is very varied, containing fundamental biotic and climatic differences within it but the different desert types need more research and analysis. The South African desert covers only 0.5% of the territory of the Republic of South Africa. The desert of South Africa borders the Nama-Karoo Biome in its eastern parts (summer-rainfall region) and the Succulent Karoo Biome in its western parts (winter-rainfall region). Some of the poorly researched high mountain peaks mapped as desert may show both climatic and floristic affinity to either the Succulent Karoo or Nama-Karoo Biomes. The unit is characterised by ecological extremes. Of all the biomes, the Desert has the lowest amounts of and the highest variability in rainfall, in places the highest ever measured temperatures in South Africa (47.8°C at a standard weather station at Goodhouse), and in other parts (western areas of the desert) the highest incidence of coastal fog. In the scientific literature, the concepts of desert vary greatly, depending on the discipline, the regional background and the viewpoint of the individual researcher. These diverse approaches result in a 'desert' varying widely from, for example, areas 'where desert pavement and varnish are common phenomena' (Evenari 1985) to dry woodlands (Evenari et al. 1985). Therefore, many vegetation scientists rather avoid terms like 'desert' and prefer to describe the vegetation structurally or functionally, e.g. by the predominance of annual plants (Rutherford and Westfall 1994).