Eco-physiological studies on desert plants : I. Autecology of Egyptian Zygophyllum species.

The Egyptian Zygophyllum species, though limited in number, contribute in considerable measure to the desert vegetation. They represent a group of succulent plants which are drought resistant or salt tolerant living under severe dry climatic conditions. Their abundance is attributed to these characteristics in addition to their unpalatibility.The distribution of the studied species is deduced from the data collected by the present authors and others working in the Egyptian desert. The growth and distribution of some Zygophyllum species are dependant on the chemical nature of the substratum. Z. occineum is a widespread species in the limestone territories of the Eastern desert. Z. decumbens is confined to a limited area within the borders of the area inhabited by Z. coccineum. Z. album is a salt tolerant plant with wide geographical range growing in dry littoral or inland salt marshes. Z. simplex, the only ephemeral species, has wide geographical and ecological ranges. The soil carbonate content does not exercise any significant effect on its distribution though it is more ecologically related to Z. occineum than the other species. Z. decumbens is ecologically related to Z. coccineum, while Z. album has its own ecological amplitude.