The Spotted Orchids of Britain and Ireland comprise just two species, one is diploid in its chromosome number and the other tetraploid. They are very closely related which explains the number of idents asked for on the internet for a photograph of one or other of these. 

Common Spotted Orchid - Dactylorhiza fuchsii

The Common Spotted Orchid is the diploid species (2n-40). 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

The diversity found in this species is noticeable. Just looking at the flowers we see background colour of virtually white, through to mid pinkish-purple. The lip markings can be light (even close to non-existent), in the form of dots and dashes, to bold, deeply coloured stripes and zigzags. The labellum will always have a large and obvious pointed central lobe. Usually there are large sinuses separating this from the lateral lobes, which typically are smaller than others of the genus. A frequent finding is that lateral lobes are reduced to a pair of oblong projections, with rounded corners. Dactylorhiza fuchsii at a particular site can show marked variability, yet also show some consistent trends. One Gloucestershire population I recall had a large number of very pale flowers, whilst another in Denbighshire was notable for bold, deeply coloured, zigzags. Obviously genes for these features were present in the plants founding the colony. The high variability of the flower appearance may contribute to the range of insects known to pollinate the species. Because fuchsii can be found so frequently and because of the range of pollinators, gene flow between populations must be quite 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. 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. It’s 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?

Heath Spotted Orchid - Dactylorhiza maculata
This is the spotted orchid that favours the neutral to slightly acid soils prevalent in upland areas. Confusion with Dactylorhiza fuchsii is a frequent occurrence – they both have similarly spotted leaves and the flower colours are likewise similar. Dactylorhiza maculata however has a much smaller central lobe to the labellum, and the side lobes are larger with round outlines. The markings are rarely as bold as can be seen on Dactylorhiza fuchsii The likeness between the two species is easily explained. Dactylorhiza maculata is an autotetraploid (2n=80) with all its genetic make-up coming from Dactylorhiza fuchsii

Polyploidy (multiple complete sets of chromosomes) in flowering plants is frequent. It is estimated that perhaps 50% of all species are tetraploid or higher. To date only one mammal has been found to be tetraploid. At meiosis one diploid germ cell would normally divide twice and produce four haploid (n=1) pollen or ova cells (zygotes). But errors during this process can yield diploid zygotes. Successful fertilisation involving two such cells will yield tetraploid progeny. Alternatively a triploid plant (n=3) may be an intermediate in the creation of a tetraploid, but triploids are prone to sterility as the balance of chromosomes at meiosis is upset. Tetraploidy can involve a single species - autopolypoloidy as in the Heath Spotted Orchids - or two different diploid species - allopolyploidy as in many of the British and Irish Marsh Orchids.

Polyploidy gives a species several evolutionary advantages. Spontaneous mutations of the genetic code are random. Most will confer no advantage to a plant, some will be detrimental, but the odd one does – and this will persist. Having four copies of each gene means that any negative effects of a mutation of one of them is minimised. During meiosis a process of chromosome cross-over can mix gene from both parents onto one chromosome. New combinations like this may give the plant an advantage, and having four sets of chromosomes increases the chances of this. Autopolyploids can be larger than either parent, so robustness and being easier to find by pollinators helps them survive, but the converse may occur with allopolyploids like the Heath spotted, as there is now an element of possible inbreeding. The new genetic make-up may confer the ability to colonise a different habitat to either parent. We can see this in the British marsh orchids. This may be due to a wider range of enzymes being capable of being produced, or double-doses of enzymes. The evidence for the evolutionary advantages of polyploidy is said to be the richness of the British endemic flora when there has been but 8000 years separation from continental Europe.

The text books tell us that Dactylorhiza maculata is represented in Britain and Ireland by sub-species ericetorum. However some of the same books can also tell us that sub-species maculata and elodes, both normally continental in distribution, can be found here. To me however, the differences seem rather minor and subjective. But I will trust the authors that the sub-species do exist. With one exception. Some authors consider there to be one species of the Spotted Orchids and refer to the Common Spotted as Dactylorhiza maculata fuchsii. This does not make taxonomic sense, putting the parent species as a sub-species of the child species. Several more grow sub-species grow on the continental mainland. Does this mean that some Dactylorhiza maculata colonies have become isolated and have diverged from the main sub-species? Possibly not! There is the possibility that autopolyploidy of Dactylorhiza fuchsii has occurred on several occasions giving rise to the continental sub-species. Their similarity is a reflection of similar parents. They are arising in different places at different times. If polyploidy can lead to speciation, it can also lead to sub-speciation. Hang on though! When discussing the polyploidy Marsh Orchids I will be stating that these are allopolyploids of the Early Marsh Orchids and (generally) the Common Spotted Orchid. Again same pairing of parents but different places and different times, but in these instances giving rise to different species – though many authors, experts and enthusiastic amateurs still have a preference for sub-species for these taxons. Ignoring that though …. if same parentage but different events can give rise to different species with notable morphological characteristics, why are they only sub-species if the differences are more subtle? Significantly DNA fragment analysis shows maculata populations to be as diverse as fuchsii, at least on continental Europe. With maculata being a much more recent species, and not having time to have evolved this diversity, the implication is that maculata may have arisen from autopolyploidy of D. fuchsii on numerous occasions.