The present book deals with the floristic composition and chorological analysis and phenology in the deltaic part and main trunk of Wadi El-Assiuty and its tributaries Wadi Habib in the central part of the Eastern Desert of Egypt. It is one of the largest and greatest dry valley which runs in this desert for a distance of about 115 km. A total of 66 species belonging to 53 genera and 21 families were recorded. Therophytes are the predominant life form and constituted 50% of total flora, Chorological analysis revealed that Saharo-Arabian (39.4%). Five species (with highest presence values) were selected to study the response of desert plants against the drought condition in desert. These are Zilla spinosa,Calligonum polygonoides, Artemisia judiaca, Leptadenia pyrotechnica and Tamarix nilotica. Ecophysiological data indicated that Zilla spinosa and Tamarix nilotica are better adapted to drought conditions prevailing in the area under study than the other species studied. This is judged by the average metabolic potentiality of both species where soluble metabolites (soluble sugars and soluble proteins) are relatively much higher than in the other plants.