The chemo-ecotone (Kamel 2003) is influenced usually by the chemical characteristic of the soil that causes the environmental gradient. The aim of the current work is to study the plants responses to overcome the high soil sodicity SAR. The impact of soil sodicity on the species distribution across the ecotone. Eleven species were selected for investigation. Soil analysis showed that SAR decreased far away from the sea gradually, causing environmental gradient. To overcome the soil salinity and sodium toxicity, the halophytes and salt resistant plants accumulated Na+ ions more than true xerophytes. All species were dependent on potassium and calcium as compatible solutes to avoid sodium toxicity. The results showed that vegetation diversity at the chemo-ecotone was controlled by soil sodicity and the ability of plants to overcome salinity. The chemo-ecotone width depended upon the ability of true desert species, Lotus hebranicus, to disperse toward the sea, as well as the true halophytes, Limonium pruinosum, toward the desert. It is concluded that the species diversity in the chemo-ecotone depends mainly on the soil sodicity as a limiting factor.