Description: This is one of the first lichens the beginner will notice on walls of limestone rock. The thallus forms flat, smooth, light grey patches, strongly zoned towards the edge. It can dominate rock surfaces, often turning considerable areas white. On close inspection, the surface will be seen to be minutely cracked into areoles (little ‘island’ pieces of thallus) in which the small, angular discs are immersed.

Key Identification Features:

• Forms white patches on calcareous rocks and walls
• Immersed discs sharply angular, the thallus zoned at the edge.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Circinaria calcarea at iNaturalist World Species Observations database.