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(Map updated: 11 August 2009)

This is a grey-coloured, black-fruited, crustose Caloplaca of hard limestone surfaces. The immersed, grey scurfy thallus is limited by a line of black prothallus. Discs are numerous, in sunken depressions and often thinly frosted, so that they can be easily mistaken for common lichens such as Sarcogyne regularis. Under the microscope the narrow spore septum separates it from similar, dark-fruited members of the genus such as C. variabilis. In Ireland, it is known from the Arran Islands.

Key characteristics

• Forms small, grey patches on, hard, well-lit, limestone boulders and surfaces
• Thallus limited by a black line; discs (to 0.5mm diam.) sunken, some frosted with pruina later leaving shallow pits; spores polarilocular, septum narrow.

Original text submitted by Vince J. Giavarini