Verrucaria macrostoma

Looking somewhat like dried and caked mud, this lichen can grow up to several cm wide and has shades of olive-green and light brown to dark brown. The thallus is cracked-areolate. Black perthecia (fruiting bodies) are not immersed in the lichen body but sit conical or hemispherical on the areoles.

It occurs on limestone, mortar, concrete, calcareous sandstones, often where there is nutrient enrichment. Widespread and common.