Description: This crustose, ‘brown Rhizocarpon’ has persistently colourless, one-septate spores, and medulla I+ blue. The epithecium is K+ purple-red and thallus C-. It is a species of hard acid rocks, especially those of mountain slopes. It is poorly recorded in Ireland, with very few records.

Key Identification Features:

• Thallus brown, areolate: C-, medulla I+ blue; spores: one-septate, colourless
• Epithecium K+ purple-red; siliceous rock – upland and coastal.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Rhizocarpon polycarpum at iNaturalist World Species Observations database.