A new locality for Crataegus ucrainica in the ravine-valley system of the River Svydnya valley (Desna basin) near the town of Krolevecz (Sumy region) has been reported. This article presents the results of a study of C. ucrainica within the species’ distribution. Based on a survey of the identified population, its ecological and coenotic features, and the ontogenetic state of the population are presented. The species is confined to areas with steep slopes, which are inaccessible for grazing, where clay deposits are exposed. The complexity of these ecotopes provides a good preservation of individuals in open meadows, forest edges, as well as in thickets of Robinia pseudoacacia and Populus alba. The coenotic affiliation of some individuals and thickets of this species to meadow-steppe, natural forest and spontaneous tree-shrub vegetation is noted. The state of the studied population in the Desna river basin is stable and sufficient for its preservation, its existence is due to the optimal hydrological regime of the slopes, which is associated with the presence of accumulated water at the bottom of valley s and a low groundwater level. The map shows the peculiarities of the distribution of the identified populations of C. ucrainica in Ukraine. A comparison of biotopes, ecotopes, soils, and vegetation types, in which populations of C. ucrainica in the area of their distribution are presented. Analysis of the seed products of this species according to analysis from different habitats allows us to assert the existence of favourable conditions for its distribution in the presence of optimal habitats.
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