Abstract. P. Delforge.- Epipactis dunensis (T. & T.A. Stephenson) Godfery and Epipactis muelleri Godfery in the British Isles [Natural. belges (Orchid. 8) 76 (1995): 103-123]. Research in Great Britain has shown that the populations of an Epipactis usually determined as E. dunensis in Northern England (Northumberland: Holy Island and South Tyne valley) and in Scotland (Lanarkshire) do not belong to the species described as E. dunensis from the Western coasts of England (Lancashire) and Wales (Anglesey). They represent E. muelleri in the British Isles. The origin of the confusion in the delimitation of E. dunensis is related. It starts with the uncertainties around the identity of E. viridiflora, and continues with two main successive errors in determinations: All Epipactis with greenish flowers are E. viridiflora and, later, All Epipactis growing on coastal sand-dunes are E. dunensis. Useful characters for the solution of the problem are given, in first place a very little used one in previous works: the colour of the base of the floral pedicel. Comparisons are made between E. dunensis (a member of the E. helleborine group) and British and Belgian E. muelleri (E. leptochila group). The presence of a still undetermined member of the E. leptochila group in the Burren (Ireland, Clare) is pointed out, with a description of its main characters.

Key-words: Flora of Britain, Scotland, Ireland. Orchidaceae, genus Epipactis, Epipactis leptochila group, Epipactis muelleri, Epipactis dunensis.