The Environment – Orchids

The following was written by Dave Bishop of Friends of Chorlton Meadows…

If you have looked at the plant life on Hardy Farm, in late May, June or early July you’ve probably noticed some very attractive plants with pink or magenta flower spikes. These plants are almost certainly Marsh Orchids.

There are a number of species of Marsh Orchid in the UK but the commonest are Southern Marsh Orchid (Dactylorhiza praetermissa), Northern Marsh Orchid (D. purpurella) and Early Marsh Orchid (D. incarnata). As the common names of the first two species suggest they tend to occur in southern and northern Britain respectively. Thus if you live in Berkshire or Cumbria (for example) you can be fairly certain about the identity of your local Marsh Orchids. But in some areas, particularly Lancashire (including Greater Manchester), Derbyshire and parts of Wales the distributions of the two species overlap; this means that on Hardy Farm and a few other parts of the Mersey Valley we’ve got both and they often grow together.

Telling the two apart around here is not easy – I keep finding plants which appear to have some of the characteristics of both species. And then there are the plants which look a bit like Early Marsh Orchid … but not quite enough to be sure. And the best examples have always been half eaten by slugs or snails. Oh dear!

Are we dealing with hybrids here? That’s the usual explanation in cases like this. Unfortunately, one of the latest books on the subject, ‘Orchids of Britain and Ireland’ by Anne and Simon Harrap (A&C Black, 2005) tells us that Northern and Southern Marsh Orchids are not as closely related as their common names suggest, and hybrids are, “surprisingly scarce”. Not only that, but the book also states that the hybrid between Early and Northern Marsh is “scarce” whilst the hybrid between Early and Southern Marsh is “rare”.

Early Marsh Orchid = Dactylorhiza incarnata

But it gets worse (or, possibly, better)! There is another species involved: the Common Spotted Orchid (Dactylorhiza fuchsii). This starts flowering towards the end of the Marsh Orchid season – but it is very ‘promiscuous’ and seems to hybridise with everything. For example, it hybridises with Northern Marsh Orchid and the hybrid, “can be common”. It is partially fertile and can back-cross with either parent to form a “hybrid swarm”. It also hybridises with Southern Marsh Orchid and can back-cross with both parents. The Harraps tell us that this hybrid is, “probably the most common orchid hybrid in southern Britain.”  Finally, the sterile hybrid with Early Marsh Orchid, “has been found scattered throughout Britain and Ireland”. At least some of these hybrids can display ‘hybrid vigour’, i.e. they are much bigger than the parent plants (I have heard them described as, “bottle-brush orchids”).

So the reason why I have so much difficulty in putting names to our Mersey Valley plants may be because they are hybrids, and even complex back-crosses, and it seems reasonable to hypothesise that many plants may well contain D. fuchsii genes. I think that our local Marsh Orchid plants may well repay closer study by an orchid expert. But such a study will depend on how much longer we’ve got them for – we’re bound to lose some if the planned football development goes ahead.

Dave Bishop, June 2009

Southern marsh Orchid = Dactylorhiza praetermissa

Northern Marsh Orchid = Dactylorhiza purpurella

Common Spotted Orchid (Dactylorhiza fuchsii)