The results of a field experiment devoted to the study of modification variability of dwarf alpine Poa section Stenopoa are presented. It is known that the steppe xeromorphic species predominantly of the southern Siberian distribution, Poa botryoides, occurs in dry steppe areas of the Altai Mountains from the lower to the upper belt. In the highlands it is replaced by a close species, even more xeromorphic dwarf P. attenuata of Siberian-Central Asian alpine distribution. During the experiment, dwarf plants from the Kurai steppe (Republic of Altai), morphologically similar to P. attenuata, were transferred to the humid conditions of Tomsk. The shoots formed under the new conditions turned out to be almost twice as tall, had wider leaves and panicles, and completely corresponded to the morphological type of P. botryoides. The experiment showed that in the Kurai steppe, near the border of the steppe and alpine belts, under the influence of specific conditions and as a result of wide modification variability, P. botryoides acquired an extremely xeromorphic appearance characteristic for P. attenuata, and occupied an intermediate position between xeromorphic and extremely xeromorphic species of evolutionary series P. stepposa - P. botryoides - P. attenuata. Since some mountain populations of P. botryoides in height and other labile morphological characters are very similar to P. attenuata, which is inherent exclusively in the alpine belt, it is necessary to search for more objective characters that allow to determine their true taxonomic affiliation. Until these criteria are found, great care should be taken when identifying the dwarf plants of this group and more attention should be paid to the ecological and geographical characteristics of both species. Apparently, in most cases, the Stenopoa bluegrasses of plains and the middle mountain belt (below the timberline), which look like P. attenuata, are the dwarf form of P. botryoides. To answer the question about the location of P. attenuata in Altai, the special studies are being conducted.
