Reviewing the lichen flora of these regions is problematic since the taxonomy is rather confused. Most of the early authors described material collected by others. Thus, they could not recognize the variability of the species. The collected material is widely spread over many European herbaria and the descriptions published in many different minor journals. There is only little synthetic work e.g. the unfinished study of Harmand (1905-1913) or recently Ozenda and Clauzade (1970). As in other arid areas, the flora is not very rich, but presence and density of species may be high in habitats favoured by frequent dew, shade and protection from the wind. In hyperarid and arid “oceanic” deserts, with dew or fog (coastal desert between Agadir and Villa Cisneros, Fuerteventura and Lanzarote, Cabo de Gata, Negev, etc.) a conspicuous biomass of lichens is developed. Most of the saharosindian lichens are reported from mountainous regions (Ahaggar, Tibesti). Travellers de scribe the central Saharan plains as devoid of lichens. Wind erosion, rarity of dew and perhaps “desert varnish” may be the main causes for this. Endemism has been probably overemphasized by misinterpretation of environ mental modifications, overestimations of minor details, or redescription of species by neglecting “concealed” bibliography.