Abstract
The Caucasus is one of the floristically richest regions of temperate Eurasia, characterized by high endemism and an exceptional diversity of rare and threatened vascular plant species. This study aims to assess the representativeness and geographical structure of rare Caucasian plant taxa preserved in the herbarium of the M.M. Gryshko National Botanical Garden of the National Academy of Sciences of Ukraine (KWHA). The study is based on a comprehensive inventory of Caucasian plant specimens, most of which were collected during the period of intensive botanical exploration of the region by Botanical Garden expeditions led by S.S. Kharkevich in the 1950s–1970s. During the inventory, species nomenclature was critically revised in accordance with modern taxonomic concepts. Protected taxa were identified based on their inclusion in the current Red Books of the Caucasian countries and their administrative regions. Chorological analysis was carried out by assigning taxa to geographical distribution types, with particular attention to endemic elements.The inventory revealed 534 taxon names represented by herbarium specimens, corresponding to 527 currently accepted species and subspecies from 270 genera and 89 families. These include one species of lycophytes, one species of horsetails, 17 species of ferns, 11 species of gymnosperms, and 497 angiosperm taxa. A total of 210 species and subspecies are protected in the countries of Transcaucasia, including 131 taxa listed in the Red Book of Armenia, 69 in the Red Book of Azerbaijan, and 52 in the Red Book of Georgia. In addition, 403 species and subspecies are protected in the Red Books of the North Caucasus, with the highest numbers recorded in Krasnodar Krai (189 taxa) and Stavropol Krai (161 taxa). The geographical structure of the studied taxa is dominated by Mediterranean, Anatolian–Caucasian–Iranian, and Caucasian distribution types, which together account for 66.6 % of the total. This pattern reflects the biogeographical position of the Caucasus within the Ancient Mediterranean region. Among the recorded taxa, 107 species and subspecies are endemic to the Caucasus. Based on the analysis of herbarium material, two new nomenclatural combinations at the varietal rank are proposed: Buxus sempervirens var. hyrcana (Pojark.) Shynder & Bahatska (= B. hyrcana Pojark.) and Lilium martagon var. caucasicum (Miscz.) Shynder & Bahatska (= L. martagon subsp. caucasicum Miscz.). These combinations allow a more accurate representation of the morphological and geographical differentiation of Caucasian populations of these species, which are currently not recognized as independent taxa. Overall, the study demonstrated that the KWHA herbarium is a key ex situ repository for the study of Caucasian plant diversity in Ukraine, particularly for rare and protected taxa.