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The Acacia desert savanna nowadays occupies large areas south of the Anti-Atlas and in the lower valley of the Draa river. The present vegetation structures are complex and constituted by elements from either tropical, either mediterranean or saharian origin, which coexist and prevail according to the present ecological and climatic conditions. At the northern border, Acacia raddiana mingles with the still mediterranean structures dominated by Argania and Euphorbia echinus whereas, in the eastern part, above 500 m, the same Acacia constitutes, with Ziziphus lotus, an essentially saharan grouping which spreads eastwards to the Saoura river valley. In the Draa depression, various sahelo-saharan trees and shrubs give to the Acacia formations the nearly similar aspect they have in the central and southern Sahara. According to the edapho-geomorphologic criteria, various associations can be defined: Balanito aegyptiacae-Acacietum ehrenbergianae in the large sand-silty areas, Foleyolo billotii-Acacietum raddianae in the silt-sandy wadis, Rottboellio hirsutae-Maeruetum crassifoliae on the rocky sanded bars and Stipagrostido pungentis-Acacietum raddianae in the large sandy wadis.