Black Lichen (Verrucaria maura) is a smooth, thin lichen with a sooty black colour, delicately cracked surface and distinctive warts. It is tolerant of periodic bathing in seawater and salt spray and is sometimes mistaken for oil. Lichen are actually a combination of algal and fungal organisms living in symbiosis. It is found in north-west Europe and forms extensive crusts over coastal rocks. This specimen was found growing on a limestone wall, 300 m from the sea..