Common Spotted Orchid - Dactylorhiza fuchsii

Undoubtedly the most common and numerous orchid species in Britain, it is possibly the first orchid you ever saw even if you didn't realise it at the time. Quite catholic in its habitat requirements, only acidic environments are probably off limits to colonisation by Dactylorhiza fuchsii. It is more dry soil tolerant than the other species discussed here.

The diversity of flower appearance found in this species is noticeable. It is possible to find colonies where a significant number of plants have notable appearance (very pale flowers, or bold magenta line designs on the labellum), but the frequency and size of colonies must mean that gene flow between them must be high. And this explains an interesting phenomenon. Dactylorhiza fuchsii has only one British sub-species, Dactylorhiza fuchsii hebridensis. This is a highly pigmented and dwarfish form found on the machair of Outer Hebridean islands, parts of Ireland and even the Shetlands. This form may persist and not be absorbed into the general population, not just because of geographical isolation, but due its significantly later flowering reducing the chance of outside genes being introduced. This ensures the integrity of the sub-species. However this subspecies has been shown to have the plastid DNA and the ITS types associated with the D. maculata species. I am surprised that this has received such little attention. Even the flower morphology is atypical of D. fuchsii and more D. maculata for me. The favored habitat though is more alkaline than liked by D. maculata and presumably it has been shown to be diploid, but personally I would "re-species" this species and find an explanation for the diploid status!
There are two varieties commonly listed; D. fuchsii o'kellyi a near white variety found in Ireland and D. fuchsii cornubiensis from Cornwall, a quite hyper-pigmented variety. These, however, have the common plastid and ITS signatures of D. fuchsii fuchsii.

The rest of the British populations will be an admixture of genes from neighbouring populations, with new colonies being created where human activity (usually) creates a new opportunity for the species to spread. Its interesting to note that the highly pigmented hebridensis distribution is similar to that of the highly pigmented D. incarnata cruenta, albeit in different habitats. Could both of these be remnants of earlier pioneer populations of their species that moved northwards following the retreating ice sheets at the end of the ice ages - until they ran out of land? Or is it an evolutionary response to a northerly climate.
British and continental D. fuscsii show general conformity of plastid haplotypes, but they are quite heterogenous when it comes to ribosomal ITS types. This suggests that there will have been some hybridisation in the past which has been absorbed into the population(s). Plants sampled for analysis from some sites show much conformity, while at other sites there is quite a mixture.

Dactylorhiza fuchsii, or rather an ancestor of the current forms, has supplied the ovules that were the maternal side of all of the British, Irish, and many of the continental polyploid Marsh Orchids; or at least that is the general thinking. However other possibilities exist for at lest some of the polyploid. D. saccifera from the eastern Mediterranean region is similar to D. fuchsii morphologically, but does have some genetic differences which can be found in at least one of the polyploid marsh orchids. It currently grows in what could have been a refugal area for Dactylorhiza species during the last glaciation. There may have been a species once common enough that was involved in the older polyploid events that is now extinct, or has been literally absorbed into D. fuchsii. A missing link for orchids.

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