To my mind the Epipactisgenus is rather fascinating. Not only do the plants and flowers themselves display a range of colours and forms based on a similar structure, but they also still pose problems of identification and species. They provide both something to admire and to think about. The recognised species are both autogamous and allogamous.
The alloogamous (cross pollinating) species are E. helleborine, the Broad-leaved Helleborine (BLH), E. atrorubens, the Dark Red Helleborine (DRH), E. purpurata, the Violet Helleborine (VH), and E. palustris, The Marsh Helleborine. The last one, though looking like a miniature tropical orchid flower, plays no further part in this ramble as it belongs to a separate sub-family to all the rest.
The autogamous (self-pollinating) species include E. leptochila, the Narrow-lipped Helleborine (NLH), E. phyllanthes, the Green-flowered Helleborine (GFH), E. dunensis, the Dune Helleborine (DH), and E. sancta, the Lindisfarne Helleborine (LH). Other entities will be introduced later. Autogamy is associated with the viscidium (the sticky blob that would attach pollinia to a visting insect’s head) disappearing before flowers fully opening, rapidly disintegrating pollinia, and incomplete flower opening.

The consensus opinion is that at the end of the last Ice Age, approximately 12,000 years ago, the Epipactoids were restricted to southern Italy. As the ice retreated the forests recolonised Europe and the helleborines followed northwards. Some populations became isolated in smaller woodlands or niche environments and evolved into the localised species that we see today. Other factors contributing towards speciation of outlying populations will include flowering time (latitude and altitude), climate, degree of isolation, and insect pollinators which are available at flowering time. Add to this the ability to form self-fertilising plants - more of this later.

The BLH is a highly variable (see here for some colour variations) and widely distributed species, and (or rather a proto-BLH) is considered to be ancestral to most if not all the other species discussed. This includes the allogamous species. Pollination will mainly be localised within a BLH community due to the insect vector, common wasps, never venturing far, there will also be seed dispersal from one community to the next thereby increasing the species gene flow and maintaining the high variability of the species. This is possible due to the widespread distribution of BLH. However this has been compromised by forest clearance and agriculture which will have fragmented the distribution across the range.
Aside from the BLH the other cross-pollinating helleborines are the VH and DRH. Compared to BLH VH shows less variantion in its genetic alleles, with some populations being mono-allelic for some of those studied. It has more tightly packed flowers than BLH and often grows in clumps. This could lead to geitonogamy - flowers being fertilised by pollen from another flower on the same plant.
DRH also have fewer heterozygotic populations, perhaps because they are growing in isolated colonies, relics of larger historical populations. Notably, whilst the UK representatives of this species seem to be confined to open limestone habitats, those on the continent are considered to be more of a woodland species. Has there been some degree of divergence due to isolation? DRH populations can be more heterogenous than VH. Some of those on Hutton Roof Crags have paler and lemon-petalled specimen for instance. However, those at Bishop Middleham were remarkably consistent in appearance to my mind.

The so-called Young’s Helleborine (YH) is a self-pollinating BLH. When first described it was considered a new species, but genetic studies have shown that the YH populations at each site it has been recorded from are much closer to the local BLH populations than they are to each other. The sites where it does grow are old coal spoil tips and are probably very different to the usual BLH habitats. These are BLH which have adapted to a new environment, perhaps by selection of a sub-population which is capable of self pollination (or something within the general BLH genetic make-up). The other distinguishing features of YH would be associated with that sub-population. Is it possible though, that at each of these sites the YH will eventually evolve into new species? Is this what happened with the LH?

Another entity to consider is E. helleborine neelandica, (NH) found in the coastal dunes of Denmark, Holland, Belgium and the top right bit of France – and South Wales (Kenfig and Oxwich). This is a plant with distinct morphology, and was originally described as a species in itself. The flower colour is a dull pink, the flower spike is short and dense, and the leaves are bunched towards the base of the stem. The latter two features can be construed as advantageous for a plant living in coastal dunes exposed to winds. However analysis of Danish plants show that like YH there is a degree of allelic heterogeny; not as much as found in typical BLH, but more than enough to demote it from a species to a sub-species at best.  Again the tight packed flowers will encourage geitonogamy and the geographic isolation has resulted in a sub-species with increased homogenicity and uniformity. What is clear is that NH is not as uniform as autogamous species like DH.
Some dispute neerlandica as being a distinct form, arguing that, like YH, it is an eco-type. It looks like it is because where it grows. There is evidence to support this view. At Kenfig some typical BLH grew in tree shade, yet when the trees were felled the Helleborines subsequently came up as NH types. My take on this is that in S. Wales there is a subpopulation of BLH, distinct from other populations, that uniquely has a habitat preference for dunes. Morphologically it is adapted to survive better there. Should it grow under a tree however, it will grow taller and have less dense flower spikes and look more like a typical BLH – just like common spotted orchids and other species grow taller and laxer in long grass or under trees. Only when that shade is removed is it able to grow as its ‘true’ form.

Other varieties are based on pigments, are rather the lack of them. BLH var. chlorantha (formerly viridis) is devoid of xanthocyanins, the blues, purples and reds that give the flowers and other parts of the plants colour. Hence it is a very green plant, even to the interior of the cup of the hypochile. Those plants which lack colouration but still have a brownish cup interior have no variety name. BLH var. monotropoides is the opposite – no chlorophyll is produced so the anthocyanins are the only pigments colouring the plants which have varying shadings of pale pink. I found a plant in the South Cotswolds that combined these two characteristics and was an overall pale straw colour. Another example may occur in South Wales. These chlorophyll deficient plants highlight the species relationship with microrhizal fungi. Normally there would be a symbiotic relationship, but without chlorophyll this is a one way relationship – the chlorophyll deficient BLH cheats on it fungal partners, taking all it needs from them and becoming parasitic.
VH var. rosea is the chlorophyll deficient variety of that species. It is white with varying degrees of magenta colouring on the leaves and stem. When there is much magenta it is very striking, looking almost like an alien life form. Some have less colouration, and indeed one of these was described to me as half-rosea. This terminology suggests that it is the amount of colour which determines a true rosea. But surely it is the lack of chlorophyll that is the true determinant?

What is interesting is that the acquisition of self-pollination is thought to have occurred independently at different times. Plasmid haplotype analysis of some European species suggests E. microphylla, a rare French species, may have evolved from a sub-population of BLH, and subsequently given rise to E. muelleri (another continental species), and both NLH and DRH. The latter is allogamous so the common ancestor to DRH and E. microphylla hadn’t converted to autogamy.
Independent of this is the evolution of the Lindisfarne Helleborine (LH), remarkably present as a population of 50-250 plants growing within 1000 sqm on Lindisfarne Island. Is this a new species limited to these dunes, a relict of a larger population, or are more colonies yet to be found? LH is autogamous and has been shown to be a distinct species, and interesting more distant from the Dune Helleborine than one might think.

The DH is another autogamous species, again restricted to a relatively few sites - or it it? See below. While it was original identified as NLH this seems to be because of its self-pollination and and open flowers. I have found no references suggesting that DH has derived from NLH; their ranges in Britain are not-overlapping by any means, and one study suggests independent evolution from BLH. When first described DH was known from west coast dune locations, hence its name. Since then however these have been increasingly found at a variety of inland sites, both in the open and in semi-shade. As all sites have plants with remarkably consistent morphological features it is quite possible that they are all derived, via windblown seed or transported soil, from one original colony. Genetic analysis should be able to support that supposition. That said, The DH has its sub-species - the Tyne variant which is found inland along the Tyne Valley. These populations do show a minor genetic difference and some different morphological features to other DH populations and are thus a distinct entity within the spectrum of DH. They seem to be tolerant of metal contamination of the soil. Is this a feature of just the Tyne variant, or do all DH have this ability and it so happens that the Tyne variant is limited to such sites by happenstance.
E. dunensis has been reported from a number of inland sites across England and Wales. Some have been known for over a quarter of a century while others have only come to light in the last few years. Personally, I am curious as to whether these populations were re-assessed from being another Epipactis species or that they are truly newly discovered. Also  are they genuinely derived from one colony, spread by either wind-blown  seed or soil importation. It seems we have an opportunity to study an endemic species’ history.
Things are complicated by suggestions that the Warwickshire E. dunensis  may be an otherwise continental species E. muelleri in fact. This is the most southerly E. dunensis site, which may have contributed to this theory, but clearly similar claims have been made before. Distinguishing between these two species is beyond me. I have no firsthand experience with E. muelleri. Close-up photos claiming to be this species on the internet seem to fall into two groups. One group looks very similar  indeed to E. dunensis, while the other looks similar but has an  arrow-shaped epichile. Authors seem to focus on different morphological  features to distinguish between the two species. Identification would  seem to be more opinion than fact. Perhaps the two species are one and  the same.

The most confusing self-pollinating species to me is the Green-flowered Helleborine. There are four  or five recognised sub-species or varienties – phyllanthes, pendula, degenera, vectensis and possibly cambrensis. I say confusing because firstly, I have not seen any papers that relate these to other Epipactis species; did it elvolve from BLH for instance. Secondly, because the morphological differences seem to overlap. BSBI records can mislead. You can find records for pendula and degenera at the exact same spot.This must be due to mis-identification. This is not surprising because at Marford Quarry I see the same plants with fully opened flowers one year, and never-opening cleistogamous buds another. The answers I want to hear is whether these varieties are close enough genetically to be considered one species, or could different evolutionary events given rise to similar looking but taxonomically distant species. I think data from continental Europe would confus things even further!

Hybridisation has been mentioned in passing. Epipactis luckily does not present the same problems regarding this as Dactylorhiza. With only three cross-pollinating species the combinations are limited. In fact, they are limited to two – BLH x DRH (E. x schmalhausenii) and BLH x VH (E. x schulzei). A DRH x VH hybrid is theoretically and technically possible, but not only do their ranges not overlap at all, but they favour habitats poles apart. The two hybrids that do occur are fertile however, so introgression with either parent is both possible and likely. Identification is often difficult.
2017 has seen some discussion regarding hybrids between Dune Helleborines and Broad-leaved Helleborines. The putative hybrids that I have seen photos of look very DH like, and are self pollinators. The two species would have to grow in close proximity, and taking the maturation of the self pollinating flower and flowering period into account, the pollen parent would need to be an early flowering BLH and the insect taking that pollen to a late flowering BLH before that plant has self fertilised. Possible yes, but how probable? The Warwickshire DH site is likely to be extensively studied for this phenomenon.

Thus within the genetics of the BLH population is the ability to change to autogamy, and this can be triggered by by the environment. The question that begs therefore is whether if an individual plant has adopted autogamy can this be temporary; just for one season. At Alyn Waters Country Park a hunt for BLH in 2013 yielded no definite examples of BLH, but there some specimens highlighted as ‘anomolies’. They had BLH features but showed evidence of autogamy with lack of viscidium and disintegrating pollinia. One possibility is is a BLH x DH hybrid. Personally I think this unlikely, despite the abundance of the second parent. These haven’t been noted in previous years by other observers. Could it be the sudden hot dry spell in early July that year triggered this change in reproduction? Could these orchids have a fall back mechanism whereby when normal fertilisation could be compromised they change to self pollination? Some GFH var pendula in Minera Quarry, which would have fully opening flowers, also showed a change; they were forming seed pods without the flowers opening fully - cleistogamy. Flowers are the means of propagating a species. Somewhere in the DNA there will be opportunities to maximise seed production when either climate or environment changes; either for a season or more permanently. If this happened elsewhere, in a situation where the conditions were the same in consecutive seasons, and we were looking at an isolated population, could we be witnessing the birth of a new variant or species? This may be what is happening with the YH and Tyne Helleborine examples and has already happened with LH.

Epipactis species show survival mechanisms for the species. Cross pollination is most advantageous because crossing produces a population with a mix of genes. Some individuals would be able to survive changes to the habitat or climate, or be able to colonise new, different habitats. Self-fertilisation takes the species down what may be an evolutionary dead end. Hybridisation, as a means of evolutionary change, ceases to be a possible event; cleistogamy, crumbling pollinia, lack of a viscidium, and non-attraction of pollinators ensure only self-fertilisation occurs, except for potential rare events. Habitat changes would probably lead to a colony dying out. The hope then for the species is that seed dispersal will find another site that is suitable for a new colony - perhaps what has happened with DH at Alyn Waters around 1990.

A feature of the Epipactis genus seems to be a predisposition to mutations of the MADS genes. These code for the layout of all the different parts of the flower. Defects include multiple columns, absent segments or double flowers. Examples of these can be seen on the Freak Show page. The same defects can be found on different plants within the same colony, suggesting a degree of inheritablility via a parent plant. Is age of the plant leading to accumulation of mutations a factor? Violet Helleborines do live a long time, and different populations across the country can show similar missing perianth segment, but as defects occur across the genus I think this explanation may only be part of the story.