The Narrow-leaved Marsh Orchid, D. traunsteineroides, can be identified by its appearance and choice of habitat. Morphologically it looks like an anorexic Marsh  Orchid. The stem is thin and looks fragile. The flowers are fewer than other of the genus and quite lax. The lip colour is purple with reddish  loops and spots contrasting, while the leaves are few, narrow as its name suggests, and held nearly erect. The lip also has a noticeable central point. The chosen habitat is calcareous fen, wetter than most others of the genus and usually those favoured by black bog rush. For  this reason its distribution in the British Isles is sporadic. There are populations with the distinctive morphology in southern England, Norfolk, Yorkshire, North Wales, Western Scotland and across Ireland. It is endemic here, though similar species occur in  Scandinavia and on continental Europe. There is a more pigmented  variation in Scotland, lapponica, which was formerly thought to be the  UK representatives of D. lapponica. Currently the Hebridean Marsh Orchid is also considered to be to be a sub-species, but I will discuss that  on its own page.

This species is an allotetraploid with D. fuchsii and D. incarnata as its  ancestors - earlier versions of those species to be more precise. It is  believed that this occurred on continental Europe during the Ice ages,  in a southern refugial area, and that the species spread northwards with the retreat of the ice sheet, perhaps prior to a similar journey to D. praetermissa. I had wondered whether D. traunsteineroides had perhaps arisen from several allopolyploidy events in the different British regions where it grows; each case giving rise to a plant with similar  characteristics capable of colonising its favoured fens. The different populations do have their specific differences, which have led to some in Scotland being called var francis-drucei and Yorkshire plants being labelled var eborensis. However nuclear microsatellite data has shown that both D. traunsteineroides and D. praetermissa have an allele present in continental D. fuchsii populations, but is absent in Britain. So as the ice retreated this species gradually colonised wet areas further and further north. After 8,000 years ago Britain was cut off from the rest of Europe. The British plants were subsequently isolated in various regions but the deciduous  forests that dominated the landscape and contributed to a dramatic  reduction in wetlands favoured by D. traunsteineroides. Meanwhile their  cousins on the continent were also isolated and are now recognised as D. traunsteineri and D. lapponica.

But hold on! The Narrow-leaved Marsh Orchid looks like upsetting both the “if it looks like a duck” philosophy, and the unsteady ground on which morphometrics sit. Further molecular analyses reveal a more complicated picture. Both plastid haplotype and nuclear microsatellite data shows  that the East Anglian and southern English traunsteineroides populations are indistinguishable from D. praetermissa populations, while those north of a line from the Severn estuary to The Wash are clearly  different. This line not only approximates well to the extent of the  Devensian ice sheet maximum, but also the southern limit of D. purpurella,

Xx

Both D. praetermissa and D. traunsteineroides have a plastid haplotype that, while absent from modern D. fuchsii, persists in continental polyploidy species such as D. majalis and D. traunsteineri.

xx
So now had do amateurs like myself view these traunsteineroides like southern Marsh Orchids. Easiest to consider them a form of D.  praetermissa that is suited for fen habitats. However, is it a case that that plants that look like this are those suitable for fen life, or does growing in a fen cause them to look like this; i.e. they are  eco-types. Otherwise the northern D. traunsteineroides do seem to be a  discrete group of populations, readily separatable from other polyploidy marsh orchids.