DESCRIPTION: Another subtle species that has a yellow-grey to bright yellowy-green thallus.  The thallus can be cracked, smooth or uneven with a  greenish-black prothallus usually seen. The apothecia can be up to 1.5mm in width and are pale yellow at first before becoming concolorous with the thallus and then black.  These apothecia are variable in shape, are somewhat convexed and have a pale-grey pruina. DISTRIBUTION: A frequently encountered species found throughout the UK.  Very common especially in coastal areas. HABITAT: On exposed nutrient-enriched siliceous rocks and walls.