Thallus a chalky white (to pale blue-grey), smooth to cracked-areolate crust, margin well-defined, usually with radial cracking; apothecia set in the thallus, with black discs, or initially grey-pruinose, one or more per areole. Often forming conspicuous, large, circular patches.

Unless identified by a recognised expert, a photo is required and the specimen should be examined with a microscope. In the comments box, state the key or ID method used and describe the size and identifying characters.

On hard limestone

All year round.

Widespread and quite frequent in Britain becoming less common in Scotland.

Widespread and fairly frequent in Leicestershire and Rutland.