A crustose lichen with a pale grey thallus that is granular or areolate. The apothecia are chestnut to rust-brown when dry, becoming dull green-orange when wet. The margin is paler, matt, and often pruinose.
Thallus: K-. Apothecia: K+ purple
In Scotland, Caloplaca ceracea is widespread on siliceous, usually shaded, maritime rocks. BLS distribution map
Caloplaca ceracea is distinguished from Caloplaca crenularia on basis of the brighter orange apothecia which become dull green-orange when wet, and by the paler, matt margins.
scottishlichens.co.uk 