The descriptive text, below the map, is from the Cornish Red Data Book (2009). The map on this web page depicts the organisms distribution and shows the records made pre-2000 and those made since.
Recorded from granite rocks and the soils overlying them, in West Cornwall and the Isles of Scilly. On the Lizard Peninsula it occurs on ultramafic serpentine rocks. In both areas the lichen occupies well-lit and very exposed situations on or near the coast. On the east coast of the Lizard Peninsula it is also found on Ash Fraxinus excelsior and Oak Quercus spp. in old/ancient woodland. Elsewhere in Cornwall it has been found on a wide variety of trees and shrubs and appears to have a predilection for Sycamore Acer pseudoplatanus . Some very large corticolous populations have been discovered in the West Penwith and Mawnan Smith areas in recent years. This very pollution sensitive species has been placed on Schedule 8 of the Wildlife and Countryside Act 1981. It has undergone a marked decline in the rest of south-west England in recent years, and Cornwall and the Isles of Scilly are regarded as the strongholds for this lichen in Britain today. It is also recently recorded in Devon, Dorset, west Somerset, west Wales and Ireland, albeit in small amounts.
I.J. Bennallick, S. Board, C.N. French, P.A. Gainey, C. Neil, R. Parslow, A. Spalding and P.E. Tompsett. eds. 2009. Red Data Book for Cornwall and the Isles of Scilly. 2nd Edition.Croceago Press.
The Cornish Red Data Book Project was led by the Cornwall and Isles of Scilly Federation for Biological Recorders (CISFBR). The full text and species accounts (minus the maps) are available on the CISFBR website.