Widely distributed on siliceous rocks, trees, Calluna stems and other acidic substrates. Characteristic hollow lobes with black, wrinkled under surface. Black pycnidia are common

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 (2011) Nordic Lichen Flora. Volume 4: Parmeliaceae