Description: Known as the ‘map lichen’ this conspicuous, mosaic-forming, crustose species has a bright yellow, mostly smooth, angular, areolate thallus, developed above a conspicuous black underlayer visible through the cracked surface and also around the margin. Discs abundant, evenly distributed, small, black, irregular. Hard acid rocks, walls and roofing slates; upland areas mainly.

Key Identification Features:

• Contrasting yellow thallus and black angular discs
• Black margins separate adjacent colonies.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Rhizocarpon geographicum at iNaturalist World Species Observations database.