The study of the form diversity of Siberian poplar species P. nigra , P. laurifolia and P. × jrtyschensis serves as the initial basis for identifying the adaptive capacity of populations, their economically valuable forms and breeding potential. The carried out analysis of the polymorphism of the species in nature and their cultivated forms showed their considerable diversity in terms of their habitual characteristics. It was revealed that the species of P. nigra , P. laurifolia and P. × jrtyschensis have been studied rather irregularly. The paper features an assessment of the form diversity in the North-Western part of the Altai-Sayan mountainous area. The analysis was performed on the basis of qualitative features of the crown, bark, leaves and shoots. Within the studied territory, P. nigra is characterized by the presence of two morphotypes, according to the nature of the pubescence and two distinct forms of bark color. It has been established that the populations of P. laurifolia of the Tom’ river basin are characterized by a greater polymorphism, both according to the diversity of morphotypes of shoots and pubescence, and by the color and structure of the cortex. The white and green bark forms of the laurel poplar are valuable for sustainable construction and selection work. In P. × jrtyschensis , gray bark forms predominate in populations, and its diversity requires a further systematic study.