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(Map updated: 11 August 2009)

This crustose epiphyte with a thin, grey to greenish thallus studded with hard, black, frosted discs (1-2mm diam.) on the bark of old, senescent oaks, is a characteristic species of very old trees in drier areas. It may occasionally spread to acid rock. In Ireland it has its headquarters in the south-east.

Key characteristics

• The habitat and the large, often crowded, more or less rounded fruits that are usually grey-frosted, serve to indicate this species
• Distinctive lichen preferring the slightly shaded dry side of trees. Often with Schismatomma decolorans.

Original text submitted by Simon Davey