Included here is the Sahara - the largest desert in the world. In an east-west axis it stretches from the Libyan Desert to shores of the Atlantic Ocean, but the northern and southern boundaries are less well defined. In the north there is a gradual transition to Mediterranean vegetation, while in the south there is a transition to tropical vegetation.

Saharan Oases

Today most oases have been used to cultivate date palm (Phoenix dactylifera) but from the remaining undisturbed remnants it seems likely that the natural vegetation of many of them would have been dominated by Hyphaene thebaica (doum palms) together with Calotrophis procera, Citrullus colocynthis (Colocynthis vulgare) and species of Acacia, Capparis, Maerua and Tamarix. For example, in small wild oases extending southeast and east from Bir Tarfawi in Egypt there are stands dominated by Hyphaene thebaica (in Bir El-Shab, for example) growing in association with Phoenix dactylifera and Tamarix nilotica with an under story of Imperata cylindrica and Juncus rigidus. These areas also include stands dominated by Acacia ehrenbergiana and the endemic Cornulaca monacantha (Chenopodiaceae). The northern edge of the Qattara Depression is also considered to be a natural oasis in a narrow zone adjacent to the escarpment. Here, however, the oasis woodland is dominated by Phoenix dactylifera but also includes Tamarix nilotica and has a similar under story to Bir El-Shab Hyphaene thebaica stand. This wild oasis also includes stands of Nitraria retusa growing in depressions and on surrounding dunes Zygophyllum nudum growing on the drier slopes. Other areas of wild oases can be found in the in the northernmost parts of the Farafra Oasis in Egypt particularly around Wadi Hennis. Here the vegetation is characterized by stands of Alhagi mannifera, Imperata cylindrica, Phoenix dactylifera, Tamaria amplexicaulis, T. aphylla and T. nilotica.

Saharan Wadis

Apart from oases, these are the only desert habitats where trees and large shrubs grow, and can be broadly divided into Acacia, Hyphaene and Tamarix communities. In fact, most of the woody species found in the Sahara belong to one of these genera. The Acacia formations usually occur on rocky beds and typically include the near endemic Acacia tortilis subsp. raddiana, A. gummifera, Balanites aegyptiaca, Maerua crassifolia and Ziziphus mauritiana as the main woody species, while the common herbs and subshrubs are Cassa italica, Caylusea hexagyna, Lavendula stricta, the near endemic Cleome Arabica (Cleomaceae), and the grass Panicum turgidum.  Tamarix communities, often dominated by T. ‘articulata’, occur in large sandy wadis. The ground between the trees is often occupied by Calligonum comosa, Leptadenia pyrotechnica and Stipagrostis pungens. Hyphaene communities are characteristic of the large wadis radiating from the slopes of Tibesti. In addition to Hyphaene thebaica, these fringing forests normally include Acacia albida, A. nilotica subsp. adstringens and Salvadora persica.

References

Bornkamm, R. & Kehl, H. 1990. The plant communities of the Western Desert of Egypt. Phytocoenologia, 19: 149-231.

Davis, P. H. 1953. The vegetation of the deserts near Cairo. Journal of Ecology, 41: 157-173. 

Houerou, H. N. Le. 1986. Northern Africa.  In: Ecosystems of the World 12B - Hot Deserts and Arid Shrubland, B. Eds. M. Evenari, I. Noy-Meir and D. W. Goodall. Elsevier.

McGinnies, W. G. et al. (eds). 1970. Deserts of the World. The University of Arizona Press.
White, F. 1983. The Vegetation of Africa. UNESCO.

Quezel, P. 1978. Analysis of the flora of the Mediterranean and Saharan Africa. Annals of the. Missouri Botanicl Garden, 65: 479-534.

White, F. 1983. The Vegetation of Africa. UNESCO.

Zohary, M. 1971. The Phytogeographical Foundations of the Middle East. In: Plant Life of South-West Asia. Eds. P. H. Davies, P. C. Harper and I. C. Hedge. The Botanical Society of Edinburgh.