Thursday, 11 June 2009

Marsh Orchids

If you’ve been walking in the Mersey Valley in the last couple of weeks you may well have encountered some very attractive plants with pink or magenta flower spikes. These plants are probably 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 in 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 (1) 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 with Southern Marsh is “rare”.

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.

The pictures above show a possible Northern Marsh Orchid (top), a possible Southern Marsh Orchid (middle) and a strange, but rather beautiful, plant that might involve Early Marsh Orchid (bottom) ... or possibly not ... Oh, I’m so confused! Help!

Dave Bishop, June 2009


‘Orchids of Britain and Ireland: A Field and Site Guides’ by Anne and Simon Harrap, A&C Black, 2005.


Polly said...

they are beautiful. I picked a couple of these up by Hardy Farm while walking the dog the other day. I put them in a vase with some buttercups, they made a fine flower arrangement for cheapskates. Felt slightly guilty about it when I googled around and found out they were orchids - perhaps they were rare and I should have left them growing. The next day, the whole vast area had been mowed! I wish I'd made a bigger bouquet now... ah well. There are still some left on the other side of the path that I will leave well alone...

Love your blog btw, just found it recently - a fascinating resource! Thanks for all the info!

Dave Bishop said...

Hi Polly,

Thanks for your comments on the blog. Welcome, and glad that you enjoy it. We certainly enjoy writing it. The thing about this medium is that when you've discovered something that is sooooo interesting that you could burst - well, you can communicate it! And if people also find it interesting, so much the better.
As for picking flowers ... well, it does tend to be a bit frowned upon these days - but, as you say, the 'licensed eco-vandals' mowed the area so we lost the orchids anyway. They are not, actually, all that rare - you've just got to know where to look at the right time of year. But always remember, if you pick a wild flower, it can't set seed - but I'm not going to get all moralistic - I bet the orchids looked great with the buttercups in that vase!