Shiny greenish olive-brown with cylindrical or branched-coralloid isidia which leave a small white scar when rubbed. Widespread and common on trunks and branches of deciduous trees, and fence posts

References: 
Thell & Moberg, editors (2011) Nordic Lichen Flora, Volume 4: Parmeliaceae
Dobson, F.S. (2018) Lichens: an Illustrated Guide to the British and Irish Species