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(Map updated: 11 August 2009)

This mosaic-forming lichen crust is characteristic of heavily shaded, siliceous rocks and underhangs. The dark, chocolate-brown thallus with violet overtones ringed in black by a conspicuous prothallus and spotted with brown, circular, powdery soralia indicate this species. It is fairly common in suitable habitats throughout Ireland.

Key characteristics

• It could only be confused with Opegrapha gyrocarpa that occurs in similar habitats. That species has powdery, usually paler orange or beige soralia that are smaller and usually less defined
• The C- reaction also separates them, Opegrapha gyrocarpa being C+ red.

Original text submitted by Simon Davey