Very similar to Pectenia plumbea and thought by some to be a hyperoceanic variant. The main differences are its larger size, the lobes display more pronounced ribbing and dark apothecia from an early stage. Mainly found on trees but also on rock

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