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The extensive lowland of Khuzistan in SW. Iran has been studied floristically. A brief information on the climate, habitat and lithology of area is presented. The hot desert of lowland along the persian Gulf area, with complex floristic situation is indicated. Their phytogeographical and taxonomic relationships are discussed in detail and attempts are made to relate the distributional patterns to certain ecological factors. 25.5% of the species are Irano - Turanian & Saharo - sindian, 22% saharo - sindian, 15.1% Irano - Turanian, 1.5% Mediterranean, 1.9% endemics, mostly derivatives of Saharo - sindian species, 6.4% cosmopolitan and 27.7% bi - or pluriregional. The highest number of endemics are found in the northern parts of the oil field areas, where they have a wetter climate than most of coastal plains.