Description: The Cypheliums are essentially stalkless ‘pin lichens’. The thallus of this species grows on epiphytic Pertusaria species (especially P. coccodes) on the bark of old oaks in open situations such as parklands, golf courses, etc. The grey thallus and black, unfrosted discs grow on the surface of the host thallus and are never immersed. The species is local but widely distributed throughout Ireland.

Key Identification Features:

• Lichenicolous on Pertusaria coccodes growing on oak in open wayside or parkland situations
• Thallus grey, discs black on the surface of the host thallus.

Original text submitted by Vince J. Giavarini

Distribution Map from NBN: Acolium sessile at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Acolium sessile at iNaturalist World Species Observations database.