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(Map updated: 11 August 2009)

This is a species of shaded, siliceous rock outcrops and dry stone walls in well-wooded hilly country. It has a scurfy, grey-green thallus and small black convex discs sometimes united to form lumpy aggregations. The spores are simple. A reddish-brown hypothecium forms a distinctive layer in the disc below an olivaceous ‘upper disc’ layer or epithecium. In Ireland, the species is rare.

Key characteristics

• Cracked or scurfy grey-green (sometimes almost black) thallus on shaded rocks below trees
• Discs small (0.2–0.5mm diam.), black with an olivaceous layer above the red-brown base layer (microscope squash to see).

Original text submitted by Vince J. Giavarini