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.
Normally this rare species occurs on trees which have nutrient-rich bark e.g. Oak Quercus spp. and Elm Ulmus agg. occurring in well-lit situations. In Cornwall it also seems to be exceptionally associated with bird-perch stones on the coast. It occurs, rarely, elsewhere in south-west England and is also known from south Wales (Pembroke) and south-west Ireland, southwards to Spain. The continued demise of the Elm, due to Dutch Elm disease, has done little to enhance the prospects for this species.
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.