Mountains hold high species diversity and endemism because of topographic diversity and isolation. Many mountainous regions are being affected by climate changes. Furthermore, mountain soils can affect plant communities by altering species components and community structure. The sub-alpine areas of western Khorassan-Kopet Dagh Mountains in the Irano- Turanian region have received little attention. We aim to provide new information on vegetation, ecological characteristics, and biodiversity drivers of plant communities associated with Cousinia edmondsonii, a very narrow endemic and critically endangered plant in NE Iran. We sampled 35 vegetation plots by stratified-random sampling in this area. Modified TWINSPAN and DCA analyses were used to classify plant communities. We used CCA analyses to assess vegetation-environment relationships and Hill numbers to evaluate diversity in plant communities. In all, 127 species were recorded, belonging to 83 genera and 29 families. The hemicryptophytes and Irano-Turanian elements were the dominant life-form and chorotype, respectively. Endemic and sub-endemic species comprised 41 species in the study area. Five plant communities types are identified in the study area based on the diagnostic and dominant species. Stipa lessingiana-Acantholimon erinaceum and Muscari neglectum-Juniperus sabina communities are dominated by thorny cushion and dwarf shrubby species, respectively. The communities dominated by C. edmondsonii, i.e., Gypsophila aretioides-Cousinia edmondsonii, Alyssum lanigerum-Cousinia edmondsonii, and Thymus kotschyanus-Cousinia edmondsonii, exhibited higher species diversity than the other communities. Based on CCA, the composition of plant communities was significantly correlated with seven topographic and environmental factors. The results showed that C. edmondsonii, its habitats, and vegetation types in the higher mountains of western Khorassan-Kopet Dagh deserve special conservation attention.

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