Lecanora carpinea (L.) Vain.
Found on the smooth-barked deciduous trees, particularly on twigs, small branches and young trees. The thin white-greyish thallus has a white prothallus. The brownish-grey discs of the apothecia are covered by thick white pruina. L. albella is very similar in appearance and is found in the same habitat, but has different chemistry
Smith et al. editors (2009) The Lichens of Great Britain and Ireland
Dobson (2018) Lichens: an Illustrated Guide to the British and Irish Species