Description: Look for this crustose lichen on large granitic outcrops or boulders. The thallus minutely cracked into tiny red-brown areoles over a black prothallus giving the whole a mysteriously dark jizz which lure the searcher. The tiny aspicilioid discs are immersed in the thallus. If you expose the medulla then try the Pd+ red test. Claurouxia chalybeioides is larger and greener and is drawn to damper rock surfaces. In Ireland, it has been recorded from the south and north-west.

Key Identification Features:

• Thallus red-brown on a black prothallus, minutely cracked; discs aspicilioid
• Looks at first like a blackish stain on the rock, medulla Pd+ red; on well-lit granitic rocks.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Clauzadeana macula at iNaturalist World Species Observations database.