Similar to Collema flaccidum but the numerous isidia are rounded. The preferred habitat is trees but not unknown from siliceous rock

Determiner: 
Neil Sanderson

References: 
Smith et al. editors (2009) The Lichens of Great Britain and Ireland
Dobson (2018) Lichens: an Illustrated Guide to the British and Irish Species
Whelan (2011) Lichens of Ireland