Bulgarian endemic <i>Carex riloensis</i>, a synonym of <i>Carex tricolor</i> (Cyperaceae): morphological and genetic evidence

Abstract Carex riloensis was described from Bulgaria as a species morphologically very similar to C. tricolor but differing significantly in the number of chromosomes. This species is regarded as endemic to Bulgaria, recorded only from the Rila Moutains and the Western Rhodopes. The goal of this study was to clarify the taxonomic status of C. riloensis through an integrative approach that includes comparative morphological, caryological, molecular phylogenetic, and genome size investigations. Morphological relationships between the examined species were tested using principal component analysis and discriminant function analysis. We also analysed the effect of DNA barcoding (ETS, ITS, and matK) on species separation. Our study revealed largely continuous variability within the group of C. tricolor and C. riloensis specimens, as well as the absence of statistically significant morphological differences between the two species. Carex riloensis and C. tricolor have identical ETS, ITS, and matK sequences, a chromosome number of 2n = 26, and identical nuclear DNA content. It is not justifiable to treat Carex riloensis as a distinct species; therefore, we propose to reduce it to a synonym of C. tricolor.