Predominantly a western species in sheltered moist areas on smooth-barked trees. Not uncommon. A member of the Lecanora polytropa group. the presence of clusters of large oxalate crystals in the thallus help distinguish it from other similar sterile crusts

References: 
Smith, C.W. et al. editors (2009) The Lichens of Great Britain and Ireland
Dobson, F.S. (2018) Lichens: an Illustrated Guide to the British and Irish Species