Description: This tiny lichen has a brown thallus tinged with mauve that is punctuated with numerous pinprick-sized spots (pycnidia). It grows only on hard siliceous rocks in the zone transitional between the black and the orange zone of the seashore. The tiny blackish discs house the three- to five-septate oblong spores (17–30µm long) surrounded by a thickish epispore. In Ireland, there are a few scattered records from the east and south-west.

Key Identification Features:

• Thallus brown, tinged mauve and sprinkled with blackish discs; dot-like pycnidia are abundant
• A species of granitic seashore rocks.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Arthonia phaeobaea at iNaturalist World Species Observations database.