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 Artemisia inculta-Carduncellus mareoticus Desert Scrub

Vegetation dominated by dwarf shrubs of Artemisia incluta and the herbaceous composite Carduncellus mareoticus can be found, for example, just south of the Mediterranean vegetation known as Thymelaea hirsuta – Plantago albicans coastal shrubland and in some cases appears to straddle the border between the Southern Mediterranean and Saharan bioprovinces. Thymelaea hirsuta can also be an important component of this desert scrub especially in non-saline depressions. In saline depressions the main associate is Atriplex halimus, while other common associates may include Haloxylon scoparium. Among the associated endemic or near endemic species are Anabasis articulata (Amaranthaceae), Asparagus stipularis (Asparagaceae), Erodium hirtum (Geraniaceae), Salsola tetrandra (Chenopodiaceae), Trigonella stellata (Fabaceae) and Zilla spinosa (Brassicaceae).

Saharan Anastatica hierochuntica-Anabasis articulata Desert Scrub

Species poor islands of this vegetation are widely distributed and can be found, for example, north and northwest of the Qattara Depression. Its average height is no more than about 5 dm and average species number is usually less than five per square metre. Anastatica hierochuntica and Anabasis articulata often grow together but in the most extreme areas the vegetation can be reduced to almost pure stands of Anabasis articulata. In less hostile areas the few other species may include Astragalus trigonus, Atriplex leucoclada, Cotula cinerea, Ephedra alata, Fagonia arabica, Helianthemum lippii, Mesembryanthemum teretifolia, Salsola baryosma, Zygophyllum coccineum and the endemic or near endemic Pituranthos tortuosus (Apiaceae), Salsola tetrandra (Chenopodiaceae), Trigonella stellata (Fabaceae) and Zygophyllum album (Zygophyllaceae). However, this vegetation tends to be of a transitional nature with certain resident species reaching their northern limit and others reaching their southern limit. The remoteness of the vegetation around the Qattara Depression means that it normally escapes from grazing by sheep or goats but is occasionally grazed by camels.

Saharan Cornulaca monacantha-Fagonia arabica Desert Scrub

Scrublands dominated by the endemic or near endemic Cornulaca monacantha (Chenopodiaceae) are widely distributed but the association with Fagonia arabica appears to be less extensive and in Egypt is mainly distributed around the Farafra Oasis. Cornulaca monacantha is the only host of the parasitic flowering plant Cistanche phelypaea and so this species also becomes a characteristic component of this formation. Other common associates depending on location include the endemic or near endemic Pituranthos tortuosus (Apiaceae) and Zygophyllum album (Zygophyllaceae), while other less common species include the near endemic Anabasis articulata (Amaranthaceae) and Tragonum nudatum (Fabaceae).

Saharan Zygophyllum coccineum-Salsola baryosma Desert Scrub

This vegetation is one of the most important precipitation-dependent communities found outside oases. It can exist in areas with precipitation less than 5 mm per annum but only where there are reliable supplies of run-off. Such conditions can be found, for example, in the piediment zones of the Abu Tartur Hills and the hills around Dakhla and Kharga oases in Egypt. Depending on location other common associates may include Astragalus vogelii, Trichodesma africanum and the near endemic Zilla spinosa (Brassicaceae). Schouwia thebaica (Brassicaceae) is also characteristic of some sub-associations. The genus of the species appears to be endemic to parts of the Sahara and Arabian Peninsula. Other associates may include Francoeuria crispa, Fagonia indica, Farsetia ramosissima, the rare Psoralea plicata, and the endemic or near endemic Anabasis articulata (Amaranthaceae) and Cornulaca monacantha (Chenopodiaceae). Some of this vegetation is known to be extremely ancient. Age determinations have shown that some of the Salsola baryosma is up to five centuries old.

South Mediterranean Atriplex halimus-Lycium europeaum Coastal Shrubland

These shrublands are characteristic of some of the more favourable parts of the coastal zone and typically found in and around wadis. They can reach heights of over 3 m but normally rarely exceed 1 m, and they can display considerable floristic variation with several different sub-associations recognized. Floristic samples have been recorded, for example, in the coastal zone just south of Mersa Matruh in Egypt. In addition to Atriplex halimus and Lycium europeaum other common species depending on locality include Periploca angustifolia, Phlomis floccosa, Plantago albicans and Salsola scheinfurthii. Phlomis floccosa (Lamiaceae) appears to be close to its western limit here and is nearly endemic to the Egyptian-Arabian BioProvince. However, much of this vegetation has been grazed, especially by goats, for thousands of years and so how close it is to the original vegetation is difficult to say. Associated endemic or near endemic species possibly include Anacylus alexandrina (Asteraceae) and Scorzonera alexandrina (Asteraceae), and several species, such as Ammochloa palaestina (Poaceae), Lobularia arabica (Brassicaceae), Paronychia arabica (Caryophyllaceae) and Verbascum letourneuxii (Scrophulariaceae) are, like the above mentioned species, possibly close to their western limit here and nearly endemic to the Egyptian-Arabian zone.

South Mediterranean Thymelaea hirsuta-Plantago albicans Coastal Shrubland

These shrublands typically occur on coastal plateaus and slopes as well as in depressions, and can be seen, for example, in the Marmarica area of Egypt. Thymelaea hirsuta can grow to heights of up to 1.5 m but is usually less the 1 m. Species composition can vary considerably and several sub-associations are recognized. Other common associates depending on locality include Atriplex halimus, Paganum harmala, Salsola schweinfurthii and Traganum nudatum, but where, for example, there are large accumulations of loose sand psammophytes like Ammochloa palaestina become conspicuous. Other less common associates include Asphodelus microcarpus, Astragalus asterias, Bupleurum lancifolium, Carduncellus mareoticus, Centaurea calcitrapa, kickxia aegytiaca,  Linaria haelava, Medicaga littoralis, Marrubium alysson, Reichardia tingitana and Salvia tetrandra. Thymelaea hirsuta is quite resistant to grazing pressure and is not browsed when green, but is commonly used for fuel, timber and shelter.

References

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