The purpose of the paper is the survey and revision o cl. C are the closest to communities of the cl. A in this subregion. However the floristic composition and ecology of plant communities of this class considerably differ from those of the cl. A. Communities of the cl. A all over its area contact with intrazonal phytocoenoses of the cl. B which are located in lower ecotopes. In the steppe zone communities of the cl. A adjoin zonal phytocoenoses of the cl. D which are spread on not salted soils of placors. The zonal semidesertic vegetation of Eurasia has still been poorly studied from the point of view of the Braun-Blanquet approach. Therefore the authors are at a loss for name of plant communities on watersheds in that zone that are contiguous with phytocoenoses of the cl. A. Communities of the cl. A are poorly investigated on the vast areas of Ukraine, Krasnodar and Stavropol territories, Don river basin, country between Don and Volga of Russia, Northern Kazakhstan.