Olive-green, wrinkled lobes with numerous warts with pale craters. Under-surface with rhizines. The red-brown apothecia have thick, warted margins. Largely a north-western species where it is widespread on twigs and branches of broad-leaved trees

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
Thell & Moberg, editors (2011) Nordic Lichen Flora, Volume 4: Parmeliaceae