Corticulous myxomycetes remain one of the least surveyed ecological groups of terrestrial protists. These organisms develop on the bark of trees, mostly feeding on bacteria and microalgae. Their microscopic size and fast developmental cycle (3–5 days) complicate the study of these organisms, and therefore data their on ecological relationships and patterns of biodiversity corticulous myxomycetes remain controversial. On the territory of the southwest spurs of the Central Russian Upland (Northeast Ukraine), no special studies on these organisms have been conducted. During 2017–2020, in nine forest sites located in this territory, we collected samples of bark of 16 species of tree plants, on which sporulating myxomycetes were then identified using the moist chamber technique in laboratory conditions. A total of 434 moist chambers was prepared, and 267 (61.5%) of which were found to contain myxomycete fruiting bodies. In total, we made 535 observations, finding 20,211 sporocarps. As a result, in the surveyed territory, we found 38 species of corticulous myxomycetes, belonging to 18 genera, 10 families, 7 orders, and 2 subclasses of Myxomycetes. Among the species of corticulous myxomycetes, the most abundant were Echinostelium minutum, Arcyria pomiformis, Macbrideola cornea, Perichaena chrysosperma, Licea kleistobolus, Paradiacheopsis fimbriata, Cribraria violacea, Enerthenema papillatum, A. cinerea, and L. operculata. The greatest species richness in the examined biota was observed for genera Comatricha, Licea, Paradiacheopsis and Perichaena, families Amaurochaetaceae and Trichiaceae, orders Stemonitidales, Trichiales and Physarales. By species diversity, dark-spored myxomycetes (Collumellomycetidae) somewhat exceeded bright-spored myxomycetes (Lucisporomycetidae). Badhamia versicolor, Didymium dubium, D. sturgisii, Macbrideola decapillata, and Perichaena luteola are new species for the surveyed area. Four species of myxomycetes were collected in Ukraine for the first time: Hemitrichia pardina, Licea floriformis, L. pygmea, and Macbrideola argentea. Quantitative and qualitative structure of myxomycete consortia developing on different species of substrate-forming plants demonstrated significant differences. The highest level of similarity was demonstrated by Fraxinus excelsior and Acer platanoides, and a relatively strong relationship was seen between Pinus sylvestris and Tilia cordata. The central cluster comprised F. excelsior, A. platanoides and P. sylvestris. By the sum of values of Bray-Curtis coefficient, Quercus robur appeared to be most distinctive plant species by quantitative composition of myxomycete consortia. F. excelsior and T. cordata are the most favourable for the development of corticulous myxomycetes. In all the analyzed consortia, the dominant species belonged to the Stemonitidales and Trichiales orders, while the remaining orders were represented by notably fewer species. Relative species richness of Stemonitidales was the highest in consortia of P. sylvestris, the contribution of Liceales was the greatest in A. platanoides and P. sylvestris, the percentage of Echinosteliales and Physarales was the highest on F. excelsior, the share of Cribrariales was especially large on A. platanoides. Trichiales were represented on all the analyzed substrates to almost the same extent. Representatives of Cribrariales and Physarales were completely absent on P. sylvestris, the species of Clastodermatales – on all species of plants, except Q. robur. Prevalence of bright-spored myxomycetes was determined for consortia of Acer platanoides, the dominance of dark-spored myxomycetes – for F. excelsior, P. sylvestris and Q. robur. The obtained data indicate the presence of stable complexes of corticulous myxomycetes, associated with different species of trees in the forest ecosystems of Northeast Ukraine. This encourages further study of the structure of myxomycete consortia with tree species that were not included in this study and determining the influence of physical-chemical properties of the bark of different plant species on the discovered peculiarities of myxomycete communities.
