Taxonomic reassessment of the British and Irish tetraploid marsh-orchids

Spasmodic progress in understanding the morphology of European allotetraploid marsh-orchids of the genus Dactylorhiza achieved in the second half of the twentieth century has in the twenty-first century been largely superseded by rapid progress in the molecular systematics of the group. However, a grand synthesis is still needed to integrate the re-circumscriptions of taxa achieved primarily through molecular data with improved identification ability derived from corresponding morphometric datasets. In anticipation of such a synthesis for the British Isles, we here summarise the taxonomic consequences of recent biosystematic research into the genus. These changes better accommodate infraspecific variation that reflects either local ecologically specialised races or especially regional contrasts in the frequency and degree of expression of anthocyanin pigments. We review recent nomenclatural changes, supporting such changes – and enacting further changes – only where they are clearly wholly unavoidable. Dactylorhiza traunsteinerioides (Pugsley) Landwehr ex R.M. Bateman & Denholm ssp. francis-drucei (Wilmott) R.M. Bateman & Denholm, comb. nov., encompasses all Scottish (and probably some northern Irish) populations of D. traunsteinerioides, including those formerly attributed to D. ‘lapponica’ p.p. and D. ‘ebudensis’; the latter becomes D. traunsteinerioides ssp. francis-drucei var. ebudensis (Wiefelspütz ex R.M. Bateman & Denholm) R.M. Bateman & Denholm, comb. nov. Also, Dactylorhiza praetermissa (Druce) Soó ssp. schoenophila R.M. Bateman & Denholm, ssp. nov., is established to encompass populations located in southeast England, south of a line from the Severn to the Wash, that were formerly attributed to D. traunsteinerioides on the basis of their gross morphology and habitat preference but have genotypes characteristic of D. praetermissa; varietal level may eventually prove more appropriate. A relatively broad morphological circumscription is recommended for D. purpurella (T. & T.A. Steph.) Soó var. cambrensis (R.H. Roberts) R.M. Bateman & Denholm. The evolutionary histories and present conservation status of British and Irish tetraploid marsh-orchids are also summarised