Species: Placopyrenium fuscellum
Photos: On walls, Macroom and Inchigeela, Cork, SW Ireland.
Pale lead-grey areolate thallus, often forming small islets among other lichens. Black prothallus visible between areoles. Mature areoles very divided by thin lines with small immersed perithecia. Thallus margin thick, can appear minutely subsquamulose.
Widespread on basic walls, mortar and calcareous rocks. Often parasitic on V. nigrescens when young. Reactions negative.
Similar: Buellia aethalea. Occurs on more acidic substrates.
Placopyrenium fuscellum (Verrucaria fuscella). August 2009