Using the traditional research methods, based on the example of local and cultivated representatives of the Tacamahaca (Spach) Penjkovsky subgenus growing in Russia and neighboring countries, the concept of a species in poplars (genus Populus L., Salicaceae) has been developed. It is suggested that the sections of black poplars (Aigeiros Duby) and balsamic poplars (Tacamahaca Spach) in Eurasia form a single supraspecific system with a common gene pool, which is very similar to syngameon. The taxonomic species that make up such a system are different dynamic states of this system and exist in the equilibrium state between natural selection, which forms and preserves the specifics of each dynamic state, and gene flows from other taxonomic species. Such a system can also be considered as a large Linnaean species represented by many subspecies or even geographical and ecological races. The use of molecular genetic methods for the taxonomic species study in the Populus genus is difficult due to the powerful flow of genes between the species, since the species differ in a small number of genes responsible for adaptive characters. The sections of the subgenus Tacamahaca poplars are ecological. The combination of species in these sections is not so much about the unity of their origin, but about the common growing conditions: black poplars tend to grow in lowlands, while the balsamic poplars tend to grow in the mountains, with which the poplars’ diagnostic characters are associated. In nature, belonging to a certain section is more profitable than the intermediate state, but in cultivation and in the urban environment, the opposite situation is observed.