For me the published field guides are of little use when it comes to hybrids, and the net is worse, with all sorts posted up with little validation. Personally I think you have to see them in real life, alongside the parent species for comparison purposes.

problem with hybrids is that some are sterile, some quite fecund, and all shades in between. There is some published work that can be used as a guide on this, but I see inconsistencies. It could be that it depends on which parent is the pollen parent. However, the naming groups, in their wisdom, have decided that when a Common Spotted Orchid hybridises with a Southern Marsh Orchid their offspring should be named Dactylorhiza xgrandis - regardless of which way around the the parentage is. It is much better to use D. fuchsii x praetermissa or even D. xfuchsermissa with the maternal or ovule parent first. The reverse paing would then be D. praeterchsii - hmmm, not so obvious. Whatever, there is no consistency here regaring which form of naming is used.

Furthermore, the `rules' should allow a pair of diploid plants (2n x 2n), if they cross, to yield fertile seed, but this is not the case for Common Spotted Orchid x Early Marsh Orchid. Harrap states the hybrid is sterile. A diploid x tetraploid cross (2n x 4n) should produce infertile seed, but not always. A 4n x 4n pairing should be fertile, but Heath Spotted Orchid x Narrow-leaved Marsh Orchid is reportedly sterile, and other pairings are of uncertain fertility. Whether they are fertile or not has different implicatications for a mixed population of Dactylorhiza.
Basically will hybrids `pollute' and take over a colony? Sterile offspring are a dead end. There will be hybrids growing, but both parent species should also be producing some pure offspring. However if the offspring are fertile, the chances of pure bred offspring can be reduced, and a whole range of mixed characteristics can be found in the colony. Should one of the parent species grow in low numbers, it could find itself dying out as a pure species.

But I have said pure species, when in fact all the molecular studies show that the Dactylorhiza species are not pure at all. they harbour DNA from old hybridisations which may either manifest as a small different in form, or yield plants that are phenologically identical to the accepted pure species.
These hybridisations can introduce alien but novel genes into a population. In tetraploid species if this gene is not beneficial it does not matter too much; It is probably harmless, and anyway they have up to three other examples doing the job. If it is beneficial, giving the hybrid an advantage over the parents, the gene will be introgressed back into subsequent generations, `improving' the species. This may be more of an aid to evolution than random mutations. In Dactylorhiza the nectar-less non-reward system of pollination by bees possibly positively encourages hybridisation. This will continue until species within populations become isolated from each other: geographically, habitat preference, non-overlapping flowering times, pollinator species etc. We should view this as a successful evolutionary strategy and celebrate it, rather than bemoan all the hybrids.

When it comes to looking at hybrids in the field it is useful to remember that they will not look like a half-way house between the parents. Usually their appearance is closer to the maternal parent than the paternal, because their will always be more maternal DNA in the hybrid. The tetraploid species have over the millennia stabilised their DNA towards that of the maternal ancestor - with exception like D. purpurella as discussed earlier. I have seen reports of artificially crossed D. xwintonii (D. praetermissa x D. incarnata) being phenologically little different to the D. praetermissa parent. I suspect the small supposed D. incarnata I see in dunes are actually hybrids with the dune forms of D. incarnata despite the flower seemingly normal.

Hybridisation, polyploidy and DNA methylation all play a part in providing us with a genus, which can baffle us sometimes, but is never boring. Such a shane we cannot look back thousands of years to see the ancestral plants, nor look forward to see what species may arise. However, we are privileged to see evolution in action in such an overt manner.