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.
Found on mossy rocks and between moss-lichen tufts on sunny, often south-facing
exposed coastal cliffs on the Lizard Peninsula, West Penwith, Pentire Head and the Isles of Scilly. More recently (2004) this lichen has been found on old, well-lit Beech Fagus sylvatica trees in Boconnoc Park. Elsewhere in Britain it is present in Pembrokeshire, on the Lleyn Peninsula, and Anglesey. It is also known from south-west Ireland, the Channel Islands and is very rare on mainland Europe with the only recent records from Brittany, France and the Algarve, Portugal. H. leucomela is a largely tropical and sub-tropical species reaching its northern limit in the U.K., where it has a southern oceanic distribution. Most populations of H. leucomela are not under any immediate threat, as the sites in which they occur are owned or managed by conservation bodies. The main threat is from the encroachment of coarse vegetation and scrub. H. leucomela is particularly sensitive to fire and the creation of firebreaks around some of the more important populations has alleviated this threat.
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.