Catapyrenium boccanum

Catapyrenium boccanum is a species of squamulose (scaley), rock-dwelling lichen in the family Verrucariaceae. It grows on mortar or on calcareous rock. Its squamules are up to 4 mm wide, pale to dark brown with black margins and a black underside. Ascospores measure 11–15 by 5–8 μm. Because of its combination of squamulose thallus, simple ascospores (without any septa), and lack of algae in the hymenium, this species is a "catapyrenioid" lichen, of which more than 80 exist in the Verrucariaceae....read more on Wikipedia.