Dactylorhiza incarnata subsp. ochroleuca
A tuberous perennial herb restricted to moist, periodically inundated calcareous fens, preferring areas of low competition that are slowly but only partially drying out. Lowland.
This subspecies, first mapped by Perring & Sell (1968), has declined over the last fifty years and is now reduced to just two populations. Even these have decreased dramatically in size in the last ten years and are now close to extinction. The plant is vulnerable to changes in water level, to deer grazing, and to scrub encroachment. It is often confused with albino variants of other D. incarnata subspecies.
European Temperate element.
RDB Species Accounts
NOTE: The account below is for the sub-species. Closely related species and sub-species may have separate accounts listed elsewhere in the Online New Atlas
Dactylorhiza incarnata ssp. ochroleuca (Wüstnei ex Boll.) P. Hunt & Summerh. (Orchidaceae)
Early marsh orchid, Mogairlean Lèana
Status in Britain: CRITICALLY ENDANGERED.
Status in Europe: Not threatened. Perhaps Endemic.
This plant of calcareous fens shows a marked preference for moist but not permanently inundated areas where there is only moderate competition. Especially, it occupies those part of fens which are in the process of slowly but only partially drying out and which are likely to have originated through a process of sedimentation. It forms distinct colonies, sometimes in association with other marsh orchids, in a rich community of fen plants including Carex panicea, Filipendula ulmaria, Juncus subnodulosus, Molinia caerulea and Valeriana dioica.
Flowering is in early June and reproduction is by seed, but its reproductive biology does not appear to have been studied in detail. With its pale cream-coloured flowers, it is easily confused with white-flowered variants of other subspecies of D. incarnata, especially ssp. pulchella.
It has been recorded with certainty from a few localities in eastern England. An old record from South Wales has never been confirmed and is considered dubious. Otherwise, all British records are from a limited area of East Anglia, and perhaps Surrey (Bateman & Denholm 1983). It formerly occurred in Suffolk at several fens in the Waveney valley but has been lost from these over the past fifty years or so. It was last seen there in about 1988 but, following a drought that year, has failed to reappear. The only certainly extant British population is in Chippenham Fen NNR, and even there numbers have fallen sharply. Ten years ago up to thirty flowering plants were recorded, but present numbers are substantially reduced and perhaps only a single clump survives.
The most serious threat to its survival lies in any widespread lowering of the water table which will upset the fine balance of its moisture requirements; an adverse threat would also be posed by prolonged inundation. Encroachment of scrub and other vegetation will also place it at a competitive disadvantage. In some years plants have been bitten off or otherwise damaged, apparently by deer, and the remaining known colony is now protected by a wire cage.
D. incarnata ssp. ochroleuca occurs widely but locally in Europe, from the Alps northwards through Germany, Poland and Estonia to Scandinavia and north-west Russia, and possibly occurs in western Ireland (Sell & Murrell 1996). As in Britain, erroneous records proliferate owing to confusion with other white-flowered forms of D. incarnata. In Scandinavia it is often afforded full specific status as Dactylorhiza ochroleuca.
M. J. Y. Foley
PLANTATT - Attributes of British and Irish plants. (.zip 1455KB) This dataset was compiled and published in 2004, and last updated in November 2008. Download includes an Excel spreadsheet of the attributes, and a PDF explaining the background and nomenclature. Note that the PDF version is the booklet as published, whereas the Excel spreadsheet incorporates subsequent corrections. A hardcopy can be purchased from the Centre for Ecology and Hydrology.