An important prerequisite for the successful introduction of rare and endangered plant species is the study of their adaptive capabilities in natural conditions. the paper presents a comparative analysis of morphophysiological characteristics (mesostructure of leaf, state of pigment complex and assimilation of carbon dioxide) of the orchid Platanthera bifolia (l.) Rich. grown in the transformed (ash dump of the Sredneuralskaya GReS) and natural (forest phytocenosis) habitats of the middle urals. It was found that orchid growing on the ash dump differed from plants growing in the forest phytocenosis by a significantly greater thickness of the mesophyll and leaf epidermis. At the same time, there was a tendency to increase the number of mesophyll cells per unit area of the leaf. there were no differences in the content of photosynthetic pigments between the studied populations. however, the assimilation of carbonic acid in the orchid from the ash dump was significantly higher than that in the natural phytocenosis. the conducted studies have shown that the revealed rearrangements in the mesostructure of P. bifolia photosynthetic apparatus contribute to the naturalization of this orchid in unfavorable ash dump conditions.