Abstract
Abstract Understanding ecological differentiation in narrowly distributed mountain endemics can clarify the factors that maintain restricted ranges and can inform conservation, even when phylogenetic relationships remain unresolved. Cousinia adenophora Juz. is a geographically restricted endemic of the western Zeravshan Range and has been treated as morphologically similar to several taxa of sect. Alpinae, particularly C. lanata, C. magnifica, and C. sarawschanica. We compared the realized environmental niche of C. adenophora with those of other morphologically similar or sectionally associated Cousinia species using climatic and edaphic variables, multivariate ordination, pairwise niche-overlap tests, and ensemble species distribution models (SDMs). In Whittaker biome space, many studied species occupied the dry temperate sector, whereas C. adenophora was confined to a relatively narrow warm and moderately dry subset. Principal component analysis revealed strong environmental structuring among taxa, with C. adenophora occupying a compact position in climatic-edaphic space. Species-centroid analysis identified C. eriotricha as environmentally closest to the endemic, followed by C. newesskiana, C. allolepis, C. trichophora, C. verticillaris, and C. xanthina, whereas C. bonvalotii, C. chrysantha, and especially C. sarawschanica were clearly separated. Univariate comparisons showed that climatic affinities were distributed among several taxa, while all examined soil variables were most similar to C. eriotricha. Pairwise niche overlap was generally low, and neither niche-equivalency nor niche-similarity tests provided significant support for shared niches. Ensemble SDMs showed high predictive performance and indicated a restricted suitability pattern concentrated in the montane belt of southern and eastern Uzbekistan. These findings demonstrate marked ecological differentiation of C. adenophora from several of the compared taxa despite their reported morphological similarity. Its narrow realized niche and restricted predicted suitability suggest potential sensitivity to habitat loss or environmental change within its limited montane range. The observed ecological pattern is consistent with, but does not by itself demonstrate, a history of geographic isolation or any particular mode of speciation. Molecular phylogenetic, population-genetic, and quantitative morphological data are needed to test these evolutionary hypotheses.