Habitats with variable watering are characterized by fairly stable illumination during the growing season, while moisture availability varies. Epilobium hirsutum L. also grows under such conditions. It is a polycarpic; clearly poly-centric juvenile of vegetative origin; geophyte; hygrophyte. The aboveground organs of this species are used for medicinal purposes, therefore the anatomical structure of the stem and leaf is described earlier. The purpose of this study is to identify the features of the internal structure of underground organs in connection with the conditions of variable watering. The underground organs of vegetatively arisen individuals are formed by sympodially growing transitional formations from the stolon to the rhizome with adventitious roots. During the study, transverse sections of the internodes of the geophil-ic part of the shoot and adventitious roots were made, and the linear dimensions of the structures were measured. It was found that the air-bearing cavities and the storage parenchyma, which occupies most of the shoot axis, are developed in the geophilic site; conductive and mechanical tissues are poorly formed. The revealed features emphasize the adaptability of the geophilic site to the implementation mainly of the functions of the supply of substances and air, vegetative reproduction and proliferation. Adventitious roots of two types, which differ in location, structure, age and functional heterogeneity.