Description: This lichen is a frequent colonist of calcareous rock as well as secondary habitats such as high boundary walls in villages, towns and cities. The brown thallus varies in colour intensity according to degree of illumination; the paler thalli are seen mostly in shaded situations. The surface is divided into an archipelago of areoles like cracked mud. Well-lit specimens are darker and so may create problems of identification with V. nigrescens which has smaller areoles and a much darker overall colour. The black perithecial discs form low, conical features that are not pit-forming or covered with an additional layer of thallus. The simple spores are in the average range 25–32mm diam.; throughout Ireland except for the far south-east.

Key Identification Features:

• Forming conspicuous, areolate crusts and blotches on walls and calcareous rock surfaces
• Like a larger, robust version of V. nigrescens; perithecia visible but almost three-quarters immersed.

Original text submitted by Vince J. Giavarini

Distribution Map from NBN: Verrucaria macrostoma f. macrostoma at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Verrucaria macrostoma f. macrostoma at iNaturalist World Species Observations database.