INFLUENCE OF THE EVOLUTION OF THE RIVER SYSTEM OF THE ALTAI-SAYAN MOUNTAIN COUNTRY ON THE FORM DIVERSITY OF MODERN POPULATIONS OF Populus laurifolia Ledeb

Populations of laurel poplar ( Populus laurifolia Ledeb . ) in the basins of the Tom and Chulyshman rivers, which are characterized by polymorphism in bark color, were studied. The most obvious morphological feature that marks these forms is the base of the leaf blade - rounded-wedge-shaped in gray bark and heart-shaped in white bark forms. The population of the river Chulyshman, differs from the plantations of the Tom’ basin by a sharp predominance of the ovate-triangular (75.5 %) shape of the leaf blade and the absence of elliptical leaves. There is a predominance of intrapopulation variability, which is typical for poplar. The interpopulation component in terms of quality features accounts for 11.8 %, in terms of phenotypes 23.8 %, which indicates the average differentiation of the studied plantations. The conducted studies have shown that the observed relationship between the blade morphology and form polymorphism is characteristic not only for the plantations of the river basin. Tom, but in general for laurel poplar. It has been established that polymorphism in different parts of the range is not an adaptation to moisture regimes, but probably reflects the distribution history of the species. The observed relationship between the populations of Tom and Chulyshman is explained by the evolution of the river system of the Altai-Sayan mountainous country. The Chulyshman River from the Oligocene to the Upper Pleistocene (30-40 thousand years ago) was part of a single river system, which also included sections of the Biya, Kondoma, and Tom. Considering that laurel poplar arose in the Neogene, and the formation of laurel poplar forests spread widely in the Middle Pleistocene, its white-bark and gray-bark forms probably populated this ancient river system even before the formation of Lake Teletskoe.