The article gives a historical overview of the formation and development of Russian phytosociology and its explicit and implicit relationships with sociology. The reasons for the using by the plant science the conceptual apparatus of sociology are considered. Both sociology and botany deal with systems that are characterized by the discrete-summative principle of organization, the activity of elements of the system and the limited resources of the external environment. These parameters condition such features of the functioning of systems as mutual influences, competition for resources (struggle for existence), selection in accordance with the criteria of fitness, development towards increasing complexity (differentiation of positions, structuring the relationships in the system, etc.), active interaction with the environment and changing the latter for the needs of the system. It is shown that the sociological metaphors used by phytosociologists were inherently tools of systemic generalizations, and have in this regard an interdisciplinary sound. The article examines the interest of P. Sorokin’s for phytosociology, for him it served as an argumentative basis in the dispute with nominalism and a source of conceptual ideas. The assumption is justified that the notion of «interaction», which is central for Sorokin’s sociology, was developed by him under the influence of reading the phytosociological works by V.N. Sukachev and G.F. Morozov. Possible theoretical connotations between phytosociological issues and research interests of modern sociology are emphasized.