A stoloniferous perennial herb of dry, species-rich coastal grasslands, often growing on cliff-slopes around rock outcrops, or on stabilised sand. It is largely restricted to exposed sites liable to drenching by salt-laden winds, and rarely occurs more than 100 m from the sea. Lowland.
T. occidentale was discovered in 1957, and described as a new species from Cornwall and the Channel Islands in 1961; populations there appear to be stable. It was found in Ireland in 1979 and in Wales in 1987, and may have been overlooked elsewhere. The Cornish populations suffer heavy mortality in hot summers but subsequently recover from seed.
Oceanic Temperate element; restricted to the coast of W. Europe.
Light (Ellenberg): 9
Moisture (Ellenberg): 4
Reaction (Ellenberg): 6
Nitrogen (Ellenberg): 2
Salt Tolerance (Ellenberg): 3
January Mean Temperature (Celsius): 6.3
July Mean Temperature (Celsius): 15.9
Annual Precipitation (mm): 940
Count of 10km squares in Great Britain: 21
Count of 10km squares in Ireland: 9
Count of 10km squares in the Channel Isles: 12
Scarce Atlas Account
Trifolium occidentale Coombe
This is a strictly maritime plant, found in dry species-rich short grasslands, rarely more than 100 metres from very exposed coasts. The soils are either shallow over hard basic or acidic rocks, or of stabilised sand. Its Welsh locality is on limestone (with Helianthemum canum); only two sites are known on shales. It extends from the spray-zone, with Crithmum maritimum, Cynodon dactylon, Spergularia rupicola and Trifolium incarnatum subsp. molinerii, to slightly less exposed grassland characterised by Jasione montana and Scilla autumnalis: in this, sparse Calluna vulgaris and Erica cinerea indicate lesser salt spray effects.
Seventy eight vascular plants were recorded by Coombe (1961) in eight 1m2 quadrats from Cornwall and Guernsey including Armeria maritima, Isoetes histrix (once), Minuartia verna, Scilly verna (infrequent) and Sedum anglicum. T. occidentale occurs on calcareous sand in Cornwall, but dune sites in north-western Guernsey are much richer: one square metre there had 39 species, including Bupleurum baldense, Mibora minima and Polycarpon tetraphyllum. Nearby, it grows with Lagurus ovatus and Matthiola sinuata. Soils range from acid (pH 5.1) on schists to alkaline (pH I 7.6) on calcareous sand. It is not found above 70 metres altitude.
It is a stoloniferous, early-flowering (late March to June) perennial, fruiting particularly where stolons extend over sunny rocks. Severe droughts kill it, as in 1959 and 1976, but on these occasions copious seedlings re-established it in 1960 and 1977. In 1990, January hurricanes destroyed many plants on western cliffs.
T. occidentale was first detected in Britain in 1957 and described, new to science, by Coombe (1961). Over three decades it has on average changed very little in distribution and abundance. It recovered slowly from local toxic detergent spillage on cliffs after the Torrey Canyon disaster of 1968. One ‘permanent’ quadrat established in Guernsey in 1959 was destroyed by a runaway oil rig in 1978.
It is frequent on the coasts of north-western France (Cotentin and Brittany) and south-eastern Ireland; and rare in northern Spain and in Portugal. For a map of its world distribution, see Preston (1980).
It is a diploid species. Spontaneous hybrids with the tetraploid Trifolium repens have not been found.
D. E. Coombe
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.
Atlas text references
Atlas Supp (20b)
1998. Trifolium occidentale D. E. Coombe (Fabaceae) in Anglesey (v.c. 52). Watsonia. 22:182-184.
1961. Trifolium occidentale, a new species related to T. repens L. Watsonia. 5:68-87.
1994. Scarce plants in Britain.