Dono-Tsimlyansk sand massif is one of the largest in the South-East of the European part of Russia. It represents a complex of river terraces of different ages within the ancient continental delta between the Tsimla and Aksenets rivers. A cluster analysis of 140 relevés was carried out using the Ward method and Czekanowski-Dice-Sørensen similarity coefficient (Fig. 4). The dataset was divided into two large groups. The first one (A) represents communities, which are formed mainly by obligate psammophytes (Table 1), many of species are used in the diagnosis of the class Festucetea vaginatae Soó ex Vicherek 1972. The second group (B) is characterized by high importance values of xerophytes and mesoxerophytes, typical for steppes and xeric meadows of the class Festuco-Brometea Br.-Bl. et Tx. ex Soó 1947. Analysis at the level of 6 clusters shows that clusters 1-4 are poorly differentiated in terms of species importance values (Table 2). Clusters 5 and 6 are clearly distinguished by groups of dominant plants. Cluster 5 represents shrub communities with mesoxerophites: Scirpoides holoschoenus, Poa angustifolia, Galium ruthenicum and Calamagrostis epigeios. Cluster 6 unites forb-bunchgrass steppes, usually dominated by Festuca rupicola, they correspond to the Festuco-Brometea. Most of the communities belong to the class Festucetea vaginatae and the order Festucetalia vaginatae. Diagnostic species of class and order (D.s.): Artemisia campestris, A. marschalliana, Astragalus varius, Chondrilla graminea, C. juncea, Euphorbia seguieriana, Festuca beckeri, Gypsophila paniculata, Kochia laniflora, Koeleria glauca, K. sabuletorum, Pilosella echioides, Secale sylvestre, Silene borysthenica, Stipa borysthenica. We identified the new alliance Agropyrion tanaiticum all. nov. D. s.: Agropyron tanaiticum, Chamaecytisus borysthenicus, Dianthus polymorphus, Holosteum umbellatum, Scabiosa ucranica, Senecio borysthenicus, Seseli tortuosum, Thymus pallasianus, Tragopogon tanaiticus, Veronica verna. Holotypus — the association Scabioso ucranicae–Stipetum borysthenicae ass. nov. The alliance unites sandy steppes with the main range in the lower Don basin. Ass. Scabioso ucranicae–Stipetum borysthenicae ass. nov. (Table 4, rel. 1–21), holotypus — Table 4, rel. 5 (field no. 22-214): Rostov Region, Tsimlyansky district, south of the Nizhengnutov village, Tsimlyansky nature reserve, gentle slope of sandy mound, 47.87754°N, 42.45692°E, 06.08.2022, author — A. Yu. Korolyuk. D. s.: Agropyron lavrenkoanum, Artemisia austriaca, Astragalus varius, Centaurea adpressa, C. arenaria, Eryngium campestre, Galium ruthenicum, Scabiosa ucranica, Seseli tortuosum, Stipa borysthenica. The association unites communities of sandy steppes, occupying leveled, well-fixed sands. It dominates the territory of the Tsimlyansky Reserve, where an anthropogenic pressure is limited. The coenoses are rich, on average 37 species per relevé, with an average cover of 40 %. The main dominant is Stipa borysthenica, its cover can reach 25–35 %. Euphorbia seguieriana and Artemisia marschalliana are constantly co-dominating. These three species form the upper layer 40–60 cm high. Agropyron lavrenkoanum, Festuca beckeri, Poa bulbosa and Potentilla arenaria are recorded in some stands with a cover of more than 10%. A moss layer is usually developed, composed of Syntrichia ruralis with a cover of up to 30 %. The association is synonymous with the subassociation Secali–Stipetum borysthenicae jurinetosum cyanoidis Demina 2009 described from Dono-Tsimlyansk sand massif. Association Secali–Stipetum borysthenicae Korzh. 1987 ex Dubyna et al. 1995 is distributed on the coastal dunes of the Black Sea and Azov; it does not occur on continental sands. Ass. Centaureo gerberi–Chamaecytisetum borysthenicae Demina 2009 (Table 5, оп. 1–36). D. s.: Agropyron tanaiticum, Centaurea gerberi, Chamaecytisus borysthenicus, Dianthus polymorphus, Thymus pallasianus, Tragopogon tanaiticus. The association represents the communities on moderately fixed sands. They form large contours, occupying slopes and tops of sandy hills, bottoms of deflation areas. The total cover varies from 15 to 60 %. Moss layer of Syntrichia ruralisis usually well developed, in some stands covering almost the entire surface. The species richness varies from 16 to 33, averaging 22 species per relevé. The set of dominant species is not constant, Artemisia arenaria, A. marschalliana, Chamaecytisus borysthenicus, Euphorbia seguieriana, Festuca beckeri, Helichrysum arenarium, Jurinea polyclonos, Koeleria sabuletorum, Secale sylvestre, Silene borysthenica are noted with a cover of more than 10 %. As part of the association, we distinguish 3 variants: typica (Table 5, rel. 1–17), Secale sylvestre (Table 5, rel. 18–24), Jurinea polyclonos (Table 5, rel. 25–36). Ass. Secalo sylvestris–Salicetum rosmarinifoliae ass. nov. (Table 4, rel. 22–30), holotypus — Table 4, rel. 28 (field no. 22-256): Rostov Region, Tsimlyansky district, south of the Nizhengnutov village, Tsimlyansky nature reserve, flat depression, 47.87348°N, 42.49095°E, 12.08.2022, author — A. Yu. Korolyuk. D. s.: Salix rosmarinifolia (дом.), Spiraea hypericifolia (дом.), Calamagrostis epigeios, Galium ruthenicum, Inula salicina, Poa angustifolia, P. bulbosa, Scirpoides holoschoenus, Secale sylvestre. The association represents shrub communities with the participation of psammophytes, occupying flat depressions in leveled and hilly sands. The coexistence in the same coenoses of Salix rosmarinifolia, common in wetlands, and xerophytic plants is typical for sandy landscapes. A characteristic feature of communities is a shrub layer composed of Salix rosmarinifolia and Spiraea hypericifolia with total cover from 10 to 35 % at a height of 80–120 cm. Among forbs the most common dominant is Scirpoides holoschoenus, less often Secale sylvestre, Galium ruthenicum, Poa bulbosa, Anisantha tectorum dominate. The moss layer with up to 15–30 % coverage was formed by Syntrichia ruralis. The class Festuco-Brometea, the order Festucetalia valesiacae and alliance Festucion valesiacae represent steppes. The suballiance Artemisio campestris–Stipenion capillatae unites grasslands on sandy soils. Ass. Scabioso ucranicae–Festucetum rupicolae ass. nov. (Table 4, rel. 31–41), holotypus — Table 4, rel. 38 (field no. 22-269): Rostov Region, Tsimlyansky district, south of the Nizhengnutov village, Tsimlyansky nature reserve, flat depression, 47.94400°N, 42.46205°E, 13.08.2022, author — A. Yu. Korolyuk. D. s.: Allium sphaerocephalon, Apera spica-venti, Centaurea adpressa, Festuca rupicola, Linaria genistifolia, Scabiosa ucranica, Stipa borysthenica, Vicia villosa. The association represents forb-bunchgrass sandy steppes. They are found along fixed sands, where they occupy periphery of flat, often extensive depressions, usually near forests and along the edge of wetlands. The coenoses are rich, with an average of 44 species per relevé and total cover from 50 to 70 %. The main dominant is Festuca rupicola, whose cover can reach 40–45 %. It forms the main layer about 30 cm high. Artemisia austriaca, Stipa borysthenica, Salvia tesquicola and Galium ruthenicum are permanent co-dominants. Agropyron lavrenkoanum, Bromopsis inermis, Carex colchica, C. supina, Euphorbia seguieriana, Poa bulbosa, Vicia villosa, Securigera varia occasionally have a high abundance.