Crustose whitish grey to grey thallus. Surface usually covered by abundant, cylindrical to coralloid isidia. Widespread and common on upland acidic rocks, especially in the north-west

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