The article discusses the anatomical structure of the leaf blade and petiole of plants of the clonal rootstock of the apple tree Kuban-86 (AP-1) depending on their growth at different altitudes of mountainous Dagestan and under urban conditions. The paratypical nature of the occurrence in an ecological-genetic experiment with clonal plants within the reaction norm is substantiated. The relationship of adaptive changes with plant growth conditions and the location of leaf attachment in the crown (sunny or shady side) is analysed, and labile and stable characteristics are identified. As taxon-specific characteristics of the AP-1 leaf the authors proposed the tortuosity of the epidermal cell walls, the types of simple and glandular trichomes, the anomocytic type of the stomatal complex, the deepening of the stomata in relation to the epidermis, the oval shape of the petiole cross-section with crenate edges, containers with a lipophilic secretion in the phloem part and the presence of oxalate drusen in the cortex parenchyma. The variability of petiole characteristics is higher than that of blade characteristics and the informative value of indicators of sclerenchyma, xylem and collenchyma tissues. The possibilities of quantitative analysis of leaf and petiole anatomical characteristics and the prospects of petiole anatomy of the hybrid AP-1 in assessing the plasticity of indicators under the influence of contrasting external conditions along an altitudinal gradient are considered. Within the crown, the specificity of changes in the anatomical structure of petiole tissues to illumination was revealed. Furthermore, the thickness of most mechanical tissues is greater in light leaves in mountainous areas and in shaded leaves in lowland areas. The latter is explained by the high light and thermal stress to which leaves on the southern side of the crown are exposed.