On the presence of Cephalanthera caucasica (Orchidaceae) in Russia: rediscovery of a threatened orchid in the Republic of Dagestan

Cephalanthera caucasica had been reported previously from the Samur Forest in Dagestan (Russia), but that report was considered doubtful: a possible misidentification of supposed hybrids between C. damasonium and C. longifolia as C. caucasica was speculated. Moreover, this species was recently reduced to a synonym of C. kotschyana in the «Plants of the World Online» database. In the present study, we did not confirm the presence of C. caucasica in the Samur Forest, but it was revealed in a few localities in remnants of beech (Fagus orientalis) forests in Kaytagskiy district and Tabasaranskiy district in the Republic of Dagestan, Russia. Living plants were studied in the vicinity of the village Tatil where 40 flowering individuals were counted. A morphological study suggested that these plants belonged to typical C. caucasica, not to any hybrid. The synonymy of this species with C. kotschyana has also been rejected, because it contradicted to the «International Code of Nomenclature for algae, fungi, and plants» and, besides, was not properly reasoned. The lectotype of C. caucasica is designated in the present paper. The description of the species is provided with measurements of the main morphological parameters. Differences of C. caucasica and the related taxa are discussed. A key to the species of the genus Cephalanthera from the North Caucasus is provided. Cephalanthera caucasica is highly threatened in Russia, being estimated as Endangered taxon (EN B1ab(iii)+2ab(iii)), according to the IUCN categories and criteria. It should be included to the next editions of both national and regional Red Data Books.