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

Determiner: 
Christine Johnson

References: 
Smith et al. editors (2009) The Lichens of Great Britain and Ireland
Dobson (2018) Lichens: an Illustrated Guide to the British and Irish Species
Ahti et al. editors (2011) Nordic Lichen Flora. Volume 4: Parmeliaceae