Pale grey, areolate thallus with broad dark prothallus. Immersed apothecia between the areoles. Common on siliceous rocks, largely maritime. Many inland records are thought to be misidentifications of Buellia aethalea

References: 
Smith, C.W. et al. editors (2009) The Lichens of Great Britain and Irelandd
Dobson, F.S. (2018) Lichens: an Illustrated Guide to the British and Irish Species
Ahti et al. editors (2002) Nordic Lichen Flora, Volume 2: Phyciaceae