Journal Number 90
March 2004

BRITISH ORCHIDS

Burnt Orchid (Orchis ustulata L.)
By David Lang

(Copyright of this paper and the associated illustrations, as well as subsequent papers and illustrations in this series, remains with the author).

Most of us involved in the study of our native orchids nurture a private passion for one particular species, and in my case it is for a charming and diminutive species, the Burnt Orchid.

Burnt Orchid is a plant of tightly grazed chalk and limestone grassland, with a range from south-east and south-central England northwards to the Dales of Yorkshire and Durham. Most populations are small. However, on a few areas of the South Downs of Sussex and the chalk hills of Wiltshire and Hampshire it can be seen flowering in thousands in the short turf. I first found it in Kent in 1953, but now I can enjoy it every early summer, living as I do in Sussex close to one of the largest populations in Britain. This is on an ancient hillfort on the Downs, and produced over 6000 spikes in 1992 - a wonderful sight. Most Burnt Orchids are small, usually 6-7cm high, with a rosette of broad leaves bearing prominent veins and several sheathing stem leaves. The bracts are reddish, and about half the length of the ovary.

The flower spike is dense and cylindrical. The unopened buds are dark reddish-brown, so the top of the spike looks burned - hence the common name. The outer and upper perianth segments form a tight hood above the pure white labellum, which has two rounded side lobes and a central lobe forked at the tip. The labellum is marked with bright crimson spots. As the flowers mature the pigmentation of the hood of the lower flowers fades almost completely, so they become white.

A late-flowering subspecies (Photo right) has been described in several countries in Europe, and the morphology described. However, this does not work in Britain, where I have found both Continental forms on the same flowering spike, so our British late-flowering form may require a new status and name. Occasionally one finds plants with unmarked labella and straw-coloured hoods. One extraordinary population in Hampshire grows in a series of damp meadows. There the flower spikes are all 15cm or more in height. Pollination is effected by a large fly Tachina magnicornis, but seed set is poor. Over the years I became aware that, although most populations flowered from mid-May to early June, I was finding the odd few plants coming into flower in July and throughout August, when the early form had set seed and vanished off the face of the earth.

The late-flowering plants never grew where the early form was to be found, and furthermore they looked different. The red colour of the hood remained red, even when all the flowers were fully opened. The labellum was more stubby, with shorter lobes, and the spots were blotches rather than discrete spots. Most striking was a deep rose-magenta flush on the edges of the labellum, which sometimes suffused the entire surface.

We now know of 16 sites for this form in Sussex, four in Hampshire and two in Wiltshire. Working on herbarium sheets in museums, I have found specimens of plants flowering in July and August dating back as far as 1870, so it is not a new phenomenon. Most populations are small, but one in Sussex regularly holds 1000 flowering plants.

The Burnt Orchid is a threatened species and populations have declined by 80% throughout their range, having gone from 210 of the 285 ten kilometre squares where it had ever been recorded. Most colonies are small, numbering a dozen or less, and are highly sensitive to grazing pressure, refusing to flower if the grass is too long but also suffering if overgrazed. Mature plants take some 16 years to grow from seed, flowering several times over the next decade. Late spring frosts can depress flowering in any one year. Careful management of nature reserves and by sympathetic farmers has stabilised some populations, but even in these cases there is little evidence of spread or recolonisation of apparently perfect habitat nearby. Chalk and limestone grassland does not take kindly to summer drought, so it remains to be seen how this little gem of an orchid will respond to global warming.

Bibliography

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