This small, prostrate, perennial sub-shrub is often abundant in short, open, rocky Carboniferous limestone grassland, on rock outcrops and on cliff edges. It typically grows in exposed S.- to W.-facing sites. 0-540 m (Cronkley Fell, N.W. Yorks.).
The distribution of H. oelandicum has remained largely unchanged since at least the 1950s. Subsp. incanum occurs in Wales and N.W. England, the endemic subsp. levigatum occurs on Cronkley Fell and subsp. piloselloides grows in W. Ireland.
Mediterranean-montane element. The species is morphologically very variable and has a highly disjunct range in Europe.
Light (Ellenberg): 8
Moisture (Ellenberg): 3
Reaction (Ellenberg): 8
Nitrogen (Ellenberg): 1
Salt Tolerance (Ellenberg): 0
January Mean Temperature (Celsius): 4.3
July Mean Temperature (Celsius): 14.8
Annual Precipitation (mm): 1108
Height (cm): 12
Perennation - primary
Life Form - primary
Clonality - primary
Count of 10km squares in Great Britain: 20
Count of 10km squares in Ireland: 10
Count of 10km squares in the Channel Isles: 0
Atlas Change Index: 0.03
Scarce Atlas Account
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
Helianthemum canum (L.) Baumg.
H. canum is restricted to Carboniferous limestone. It is found on rocky outcrops and on the face of scars and cliffs, often on the upper parts of outcrops and in sparse vegetation on shallow soil near the edges of cliffs. It can be very abundant on steep, rocky, exposed, often south-facing sites, which are prone to summer drought. Its associates include a number of typical limestone plants, particularly Anthyllis vulneraria, Helianthemum nummularium, Hippocrepis comosa, Lotus corniculatus, Scabiosa columbaria and Thymus polytrichus. In Teesdale it is found on sugar limestone, an extremely porous and free-draining metamorphosed Carboniferous limestone. It is almost exclusively lowland but occurs at 535 metres on Cronkley Fell.
H. canum is a shrubby, mat-forming perennial. Plants flower freely and set abundant seed unless they are subjected to particularly heavy grazing. There is no specialised means of dispersal. Seeds produced in one summer germinate gradually over a long period but the successful establishment of seedlings requires a period of damp weather long enough for young plants to develop a root system which will withstand subsequent drought (Griffiths & Proctor 1956).
Its major British stronghold is on the Great Orme. Some smaller populations may be threatened by competition from invading native trees and shrubs, and aliens such as Cotoneaster spp. and Rhamnus alaternus.
H. canum is also found on the west coast of Ireland, central and southern Europe, Oland (Sweden), Asia Minor, the Caucasus and North Africa.
Two subspecies are recognised in Britain. The widespread plant is subsp. canum which occurs almost throughout the range of the species. The plant on Cronkley Fell is an endemic subspecies, subsp. laevigatum M. Proctor.
Atlas text references
Atlas Supp (11a)
1988. The Irish Red Data Book. 1. Vascular Plants.
1956. Helianthemum canum (L.) Baumg. In: M. C. F. Proctor, Biological Flora of the British Isles. No. 58. Helianthemum Mill. Journal of Ecology. 44:677-682.
1986. Atlas of north European vascular plants north of the Tropic of Cancer. 3 vols.
1978. Vergleichende Chorologie der zentraleuropäischen Flora. Volume 2. 2 vols.
1994. Scarce plants in Britain.
1999. British Red Data Books. 1. Vascular plants, edn 3.