The Epipactis helleborine Group (Orchidaceae): An Overview of Recent Taxonomic Changes, with an Updated List of Currently Accepted Taxa

The Epipactis helleborine (L.) Crantz group is one of the most taxonomically challenging species complexes within the genus Epipactis. Because of the exceptionally high levels of morphological variability and the ability to readily cross with other species, ninety different taxa at various taxonomic ranks have already been described within its nominative subspecies, but the taxonomic status of most of them is uncertain, widely disputed, and sometimes even irrelevant. The present review is based on results of the most recent research devoted to the E. helleborine group taxonomy. In addition, we analysed data about taxa belonging to this group presented in some research articles and monographs devoted directly to the genus Epipactis or to orchids in certain area(s). Based on the reviewed literature and data collected in four taxonomic databases available online, we propose an updated list of the 10 currently accepted taxa in the E. helleborine group (two species, six subspecies, and two varieties), which includes E. helleborine (L.) Crantz subsp. helleborine; E. helleborine subsp. bithynica (Robatsch) Kreutz; E. helleborine subsp. distans (Arv.-Touv.) R.Engel and P.Quentin; E. helleborine subsp. neerlandica (Verm.) Buttler; E. helleborine var. tangutica (Schltr.) S.C.Chen and G.H.Zhu; E. helleborine subsp. tremolsii (Pau) E.Klein; E. helleborine subsp. voethii (Robatsch) Jakubska-Busse, Żołubak, and Łobas, stat. nov.; E. condensata Boiss. ex D.P.Young; E. condensata var. kuenkeleana (Akhalk., H.Baumann, R.Lorenz, and Mosul.) Popovich; and E. cupaniana C.Brullo, D’Emerico, and Pulv.