Parmelia omphalodes (L.) Ach.
Foliose, variable in colour olive brown to dark brown or grey, green-tinted when shaded or wet. Conspicuous, white pseudocyphellae on the lobe surfaces. Apothecia with dark-brown discs and pale, crenulate margins. Common in the north-west on exposed base-rich rocks
Dobson (2018) Lichens: an Illustrated Guide to the British and Irish Species