Thursday, 9 June 2016

More Marsh Orchids, This Time Southern and Early

Statistics might prove me wrong but by shear volume of visitors, many on large charabangs on day trips, Bourton-on-the-Water in the summer is probably the most popular tourist spot in the northern Cotswolds.  We don't like crowds and as a result we hardly ever go there, but I have now found a very good reason to visit. On the outskirts is a Gloucestershire Wildlife Trust reserve, Greystones Farm which includes the Salmonsbury Meadows SSSI, a wet meadow, on the banks of the meandering River Eye - wonderful on a bright early summer day as today was.  

The meadow has decent populations of Early Marsh Orchid (Dactylorhiza incarnata ssp incarnata - the pale pink form) and also Southern Marsh Orchid (D. praetermissa).   The variability of marsh orchids is curious.

Of the 6 species of Marsh Orchids (Dactylorhiza) in Britain, in my experience 2 show little morphological difference and are unmistakeable (Northern Marsh and Early Marsh - other than the readily recognisable subspecies which are different colour forms), but others such as Common Spotted, and Heath Spotted are very variable both in the colour, spotting on the leaves and marking on the labellum.   They also seem to be catholic about their preferred habitats.  (I commented on the taxonomic issues with Narrow-leaved in an earlier post).   Southern Marsh also seems to show variability;  I saw a deep magenta form on the A34  two weeks ago, and whilst the plants I saw today had a consistent paler hue the labellum shape and the degree of spotting on the leaves were variable.   New Flora of the British Isles ("Stace") has it that the leaves are usually unspotted, with a labellum which is shallowly 3-lobed.  

Between 10 and 20% of the plants at Greystones were spotted.  Are the spotted ones true to the species, or has there been some introgression with Common Spotted, though I found no plants of the latter on the meadow?  The labellum shape was variable, but there seemed to be no correlation between shape and whether or not the leaves were spotted.  The other characteristics matched up to the description in Stace.  Both the spotted and unspotted leaves had a few stomata along the veins of the upper surface of the leaves, consistent with Southern Marsh -Vegetative Key to the British Flora ("Poland"); by contrast Common Spotted only have stomata on the lower surface.   My conclusion therefore that these were in fact all Southern Marsh but the spotting may be due to variability or a small degree of introgression.

Nearby plants included Meadow buttercup, Ribwort plantain, Creeping cinquefoil, Red clover, Fescues, Hard rush, Meadowsweet, Silverweed, Hairy sedge, and Common mouse-ear.

There was plenty of non-botanical interest: inter alia lots of Blue Damselflies, Beautiful Damoiselles and on the Lakes, a close-up of a Great Crested.

I came home via Upper Slaughter; three weeks ago the emerging orchids there were only in leaf.  Using Poland I had them down as a mix of Common Spotted and Southern Marsh.  I went back today to see if I was correct.   Actually not quite.  They all had the appearance of Southern Marsh but about 50% had quite heavily spotted leaves.  I came to the conclusion that even though there were no Common Spotteds around these were  hybrids, D. x grandis (leaves had no stomata on the upper surface, and edge in parts like that of Common Spotted - Poland again).  The flowers had more the shape of Southern Marsh.  Here's an example: 

I will try to give orchids a rest now for a day or too. Orchid non-enthusiasts can rejoice in that it is quite a short season.

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