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 Halogypsophilous Vegetation

This salt tolerant vegetation is mostly confined to depressions devoid of any drainage and as a result subjected to high levels of evaporation. Salt from sub-surface strata is brought to the surface by capillary action. In hypersaline situations the extreme halophyte Halocnemum strobilaceum may be the only species present, but in less demanding situations species such as Limonium pruinosum, Nitraria glaucum, Salsola sieberi, Suaeda mollis, Zygophyllum cornutum, the endemic Arthrocnemum glaucum (Chenopodiaceae) and Limoniastrum guyonianum (Lamiaceae) and near endemic Salsola tetragona (Chenopodiaceae), Traganum nudatum (Chenopodiaceae) and Zygophyllum album (Zygophyllaceae) be can be found but there is some regional variation.  Where gypsaceous loamy sands occur a new suite of species are encountered often dominated by Salsola baryosma and the near endemic Suaeda vermiculata (Chenopodiaceae). Other associated species include the endemic Lycium inticatum (Solanaceae) and Nucularia perrinnii (Chenopodiaceae) and the near endemic Atriplex halimus (Chenopodaceae). 

Saharan Zygophyllum coccineum-Schouwia thebaica Saline Desert Scrub

Vegetation characterized by these two species covers large parts of the Western Desert and is well represented in and around the Qattara Depression, which is up to 135 m below sea level. However, runoff from the surrounding escarpments increases the level of water available. Zygophyllum coccineum is the main pioneer species sometimes forming almost pure stands but in distinctly saline areas the endemic or near endemic Zygophyllum album (Zygophyllaceae) may also be present usually growing on the margins. Schouwia thebaica is a desert annual of the Brassicaceae family. The genus Schouwia appears to be endemic to the Sahara and parts of the Arabia Peninsula. Other common associates depending on locality include Capparis leucophylla, Pergularia tomentosa and Zygophyllum simplex, while in the inner margins of large depressions the endemic or near endemic Acacia raddiana (Fabaceae) may become established. Other endemic or near endemic taxa associated with this vegetation include Cleome droserifolia (Cleomaceae), Monsonia nivea (Geraniaceae) and Trigonella stellata (Fabaceae). Grazing in the Qattara Depression is mainly restricted to the camels of Bedouins since the nearby Qara population is mainly based on crop cultivation.

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.

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.