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