The Northern Marsh Orchid, D. purpurella, is widely distributed across the British Isles north of a line corresponding to the maximum extent of the Devensian ice sheet - roughly from The Wash to the Severn Estuary. Often a large stocky plant, when growing in rabbit cropped turf it can be quite short. The flowers are usually densely packed in a columnar spike. The lip is shield-shaped, moderately deeply coloured purple, with bold magenta lines and dots.

D. purpurella has a plastid haplotype that is present in a consistently high frequency. This haplotype has probably derived from one that is  dominant in British populations of D. fuschsii. Thus it would seem that D. purpurella occurred as a result of a single alloploid event shortly  after the retreat of the ice sheets in Britain, and then spread northwards, and presumably across what was Doggerland to western Scandinavia where it is also found, albeit in small numbers. Are these really from the same ancestral stock as the British plants? It would be nice to see some molecular comparisons, though there would  have been some divergence in the 8,000 or so years since the North Sea  flooded the low-lying land between here and Scandinavia. Currently D. purpurella could be considered a former endemic species.

So what of the Welsh Marsh Orchid, currently designated D. purpurella ssp cambrensis? The one molecular study that included this only sampled two populations (but there are not many to choose from), and the overall results placed it firmly within the bounds of D. purpurella. In one part of the study, the DNA Internal Transcribed Sequences, the Welsh Marsh Orchid  did differ from the Northern Marsh Orchids studied. D. cambriensis had 63% ITS V and 37% ITS X, while for D. purpurella the figures were 25% and 75% respectively. Based purely on the ITS data D. cambriensis  is as distinct from D. purpurella as D. praetissima is from D. traunsteinroides, but this is on limited sampling and just one factor. For me this suggests that cambriensis is a distinct and originally local variety of D. purpurella. I am quite content with this. In appearance those plants I have seen and consider as possible Welsh Marsh Orchids are clearly different in  appearance to Northern Marsh Orchids. What is important is that the  study shows that there is such an entity. What is demonstrated that this population is not a hybrid mix of D. purpurella and D. fuchsii - D. x venusta. The hybrid certainly exists, but so does the Welsh Marsh  Orchid. That the latter has some features that one would expect of the  orchid could purely be coincidence.

Originally found on Welsh coastal dunes, the Welsh Marsh Orchid seems to have been branded as a dunes-only species - much like the Dune Helleborine. However, I believe it, just like the helleborine, to have a much wider range both geographically and in terms of habitat. What is puzzling is that where it grows it share the location with Northern Marsh Orchids. Do they hybridise, if that term can be used for within a species? If so the progeny may be represented by some of the less typical Northern Marsh Orchids on site.