Description: To find this rarity you would need to search the stems of Calluna in among the Atlantic blanket bogs and coastal rocky heath of western Ireland. At UK sites it often grows on rowan. Like A. spectabile (described elsewhere) this small, freckled crust (<3cm diam.) forming tiny patches is white to grey in colour. The vaguely rounded discs (0.3-0.6mm diam.) are black and slightly convex but lack a surface frosting of pruina. A. spectabile is very similar, but has much larger discs to 1.2mm diam.

Key Identification Features:

• In Ireland, it is restricted to the stems of Calluna plants growing on the Atlantic coast
• Forms tiny grey-white patches with a black freckling of miniature roundish discs without pruina; spores muriform.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Arthothelium norvegicum at iNaturalist World Species Observations database.