Bili Skeli limestone cliffs as an important hotspot of plant diversity in the Chyvchyny Mountains (Ukrainian Carpathians)

: In this paper we present the flora of Bili Skeli (White Cliffs) Massif. This site is the southernmost group of limestone cliffs in the Ukrainian Carpathians, situated in the montane forest belt in the headwaters of the Bilyi Cheremosh River (Verkhovynskyi National Nature Park, the Chyvchyny Mts.). These cliffs harbour rare calcareous saxicolous species, e.g. Arabis hornungiana, Carduus defloratus subsp. glaucus, Cystopteris alpina, Epipactis atrorubens , E. helleborine , Goodyera repens, Saussurea discolor, Saxifraga luteoviridis and Thymus pulcherrimus , many of them included in the Red Data Book of Ukraine (2009). Their occurrence was analysed in their ecological and conservation context. A map of the site is provided as well as geographical coordinates of the major cliffs. The occurrence of obligatory calcicole rare species is determined by the limestone bedrock, which is infrequent in the Ukrainian Carpathians. The rarity of the habitat type makes the site one of the few disjunct environmental islands of calcareous flora in the region. Some of the listed species are narrow-range and occur at the edge of their geographical distribution. Moreover, Saussurea discolor is confined to the lowermost limit of its altitudinal range. Such marginality makes the area remarkable in biogeographical and conservation terms. It was revealed that a population of another rare species, Saxifraga aizoides , has possibly become extinct at this site. However, the confirmed occurrence of Saussurea discolor makes the Bili Skeli cliffs the second (in addition to Chonyi Dil Mt.) known locality of that species in the Ukrainian Carpathians.