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.
Photograph of Verrucaria macrostoma, taken March 2012 on old canal coping stone, Staffordshire. © Pete Hillman 2012. Camera used Panasonic Lumix DMC-FZ38.