Description: The thallus of this dark grey to dark brown crustose lichen is rather small and areolate (cracked like a mirror), and scattered over the tops and sides of nutrient-enriched siliceous rocks and boulders. The colourless, muriform spores (usually two spores per ascus) and K- epithecium separate it from R. geminatum which has brown spores and grows in an altogether different habitat. In Ireland, it is known on rocks in Connemara but is likely to occur more widely.

Key Identification Features:

• Thallus, areolate, mostly brown-coloured; tops and sides of granitic rock
• Epithecium K- (with green glow), asci one- to two-spored (occasionally four-spored); spores persistently colourless.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Rhizocarpon subgeminatum at iNaturalist World Species Observations database.