A rhizomatous perennial herb occurring in a range of wetland habitats, including lakeside reed-beds, sedge swamps, Salix carr, river banks and wet meadows; also, in S.W. Scotland, at the base of coastal cliffs where streams emerge and along the upper edge of fringing saltmarshes. 0-300 m (Clearburn Loch, Selkirks.).
There has been little change in the distribution of H. odorata since the 1962 Atlas, though it is now known to be frequent in Orkney, where it was first recorded in 1980, and where all sites are near Norse church sites. It is abundant at its only site in Ireland, on Lough Neagh.
Circumpolar Boreal-montane element, with a continental distribution in W. Europe.
Count of 10km squares in Great Britain: 18
Count of 10km squares in Ireland: 1
Count of 10km squares in the Channel Isles: 0
Atlas Change Index: 0.39
RDB Species Accounts
Hierochloe odorata (L.) P. Beauv. (Poaceae)
Holy-grass, Feur Moire
Status in Britain: LOWER RISK - Near Threatened.
Status in Europe: Not threatened.
H. odorata is a rhizomatous, perennial grass of northern latitudes with a curiously disjunct distribution in Scotland and Ireland. Its habitats in Scotland include base-rich fen (Blackpool Moss), raised mire (Ale Water), maritime grassland at the upper limit of tidal saltmarsh (Southwick), lakeside willow carr and sedge communities (Loch Leven), river bank (Thurso), and the base of coastal cliffs in thin, peaty saltmarsh over shingle and boulders (Ravenshall). The species, therefore, has an extremely long and unusual list of associated species, ranging from Festuca rubra and Juncus maritimus through Deschampsia cespitosa, Molinia caerulea and Schoenus nigricans to Filipendula ulmaria, Phalaris arundinacea and Phragmites australis. In south-west Scotland the sites are exclusively coastal and close to the high water mark of spring tides, but inland in the Borders, H. odorata grows up to an altitude of 260 metres. The main common features of all habitats are the generally high water table and usually base-rich soils.
Flowering occurs between March and May and appears to vary considerably. In many sites this may depend on the lowering of high water tables from year to year - the plant being fully submerged for much of the winter. When not in flower, the characteristic bright green leaves are a help to finding the grass, which may be easily overlooked. The aromatic leaves contain the distinctive (almost Briza-like) pyramidal panicles containing many glistening spikelets, each with one terminal hermaphrodite floret and two lower male florets. Six clones sampled from Scotland were tetraploid and although seed-set was low (around 2%), isozyme electrophoresis indicated that there is genetic variation in British populations (Ferris, et al. 1992). Most populations show irregular male meiosis and a remarkable mixture of first and second division restitution (a cell failing to divide despite the chromosome replicating). Such irregularities produce unreduced or polyploid gametes and help to account for the low seed production.
The known sites of this grass have been well mapped and characterised and most seem to have well-established, if small, clones which do not vary much in size from year to year. In some populations (e.g. Blackpool Moss, Ale Water), the extent of the clone(s) is very marked whilst in other areas (e.g. at Ravenshall) the distribution appears to be patchy. Some such clones are large (at Southwick Merse plants are scattered within an area more than 160 x 30 metres), others are discrete and not obviously connected.
It is difficult to know what the main threats to H. odorata may be, or indeed whether they are common from site to site, but the plant appears to flourish in open areas where grazing prevents grassland from becoming too dense. Invasion of the sites by Ulex europaeus (in the grassland at Southwick) and by Salix species (at Blackpool Moss and Portmoak Marsh, Loch Leven) may be a threat. Plants in cultivation are sensitive to drying out and both drainage of wetlands and erosion of fringing saltmarsh are likely to be major threats to specific populations. Most known sites are protected in SSSIs.
H. odorata occurs in northern and central Europe, southwards to the Alps and Moldavia, northwards to Iceland and Fennoscandia, and eastwards to northern and central Russia. It is rare in several countries, and endangered in Switzerland.
A. J. Gray
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.