Images of British Lichens
Rimularia limborina Nyl.
Thallus grey to dark brown or black, matt, cracked-areolate with the black prothallus often visible between the areoles; apothecia black, sometimes somewhat folded (gyrose), margins thick, often cracked. Widespread but very local on upland siliceous and basaltic rocks.
Refs: Smith et al. (2009), 811; Purvis et al. (1992), 543.