A tufted perennial grass of open, sheep-grazed turf around rock outcrops on S.-facing Carboniferous limestone slopes. Its sites are characterised by high levels of insolation and summer drought. Lowland.
In the British Isles K. vallesiana has always been restricted to the Mendip hills (N. Somerset). It was first collected in this area in 1726, but not recognised until it was rediscovered by Druce in 1904. It was introduced to Goblin Combe (N. Somerset). Its distribution is stable.
Suboceanic Southern-temperate element.
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Light (Ellenberg): 8
Moisture (Ellenberg): 1
Reaction (Ellenberg): 8
Nitrogen (Ellenberg): 1
Salt Tolerance (Ellenberg): 0
January Mean Temperature (Celsius): 4.5
July Mean Temperature (Celsius): 16.4
Annual Precipitation (mm): 868
Height (cm): 40
Perennation - primary
Life Form - primary
Clonality - primary
Count of 10km squares in Great Britain: 4
Count of 10km squares in Ireland: 0
Count of 10km squares in the Channel Isles: 0
RDB Species Accounts
Koeleria vallesiana (Honck.) Gaudin (Poaceae)
Somerset hair-grass, Cribwellt Oddfog
Status in Britain: LOWER RISK - Near Threatened.
Status in Europe: Not threatened.
K. vallesiana has a remarkable history in Britain. It was first discovered by Dillenius in 1726 at Uphill and Brean Down, but his notes and specimens subsequently became separated. It was collected again in 1773 by Rev. Lightfoot, but its identity remained unknown, and it was not until 1904 that Druce, working on the memoirs of Dillenius, made the connection between notes and specimen and was able to verify the presence of the grass at Uphill. Although not a particularly critical species, it was not recorded further east of Crook Peak in the Mendips until some 50 years later, and was recorded at Sand Point for the first time as recently as 1974.
It grows in thin, open, often rocky turf on generally south-facing Carboniferous limestone slopes. Although its sites experience mild, wet winters, the summers are harsh, with high levels of insolation, low rainfall and parched soils. The limestone turf is characterised by such typical associates as Pilosella officinarum, Sanguisorba minor and Thymus polytrichus dispersed around tussocks of Festuca ovina. Particularly striking is the representation of annuals and pauciennials, including Blackstonia perfoliata, Carlina vulgaris, Centaurium erythraea and Euphrasia nemorosa. Carex humilis and Potentilla neumanniana also occur in the community.
It is a tufted perennial grass, superficially similar to the widespread K. macrantha, but its stems are swollen at the base, with a thick covering of the fibrous remains of old leaf shoots. Flowering is from late May to July.
The distribution of K. vallesiana closely matches that of Helianthemum apenninum and Trinia glauca. It is currently known at about twenty sites in eleven 1 km squares on the southern slopes of the Mendip hills, from Brean Down on the coast inland to Shute Shelve and Fry's Hill. In recent years, intensive searches have shown that this species has been lost from four further sites. In at least six of its major sites populations of K. vallesiana number in the thousands. Most sites are adequately protected, though not all are grazed by livestock. Sheep are ideal grazers, but it is clear that rabbits are important in maintaining a thin, open turf. It is likely that in the more steep and rocky locations the extreme microclimate is sufficient to maintain suitable conditions in the absence of grazing. The species is thus in little immediate danger. It has been introduced to Goblin Combe (Hope-Simpson 1987).
The hybrid with K. macrantha has been reported from most of the K. vallesiana localities. It is sterile and apparently not known outside Britain (Stace 1991).
K. vallesiana has its stronghold in southern Europe from the Iberian peninsula to Italy, and also occurs in north-west Africa. It reaches its northern limit in England, is rare in Switzerland and endangered in France.
R. D. Porley