Caloplaca littorea Tav.
Thallus crustose, in small to extensive patches, more or less cracked-areolate, bright yellow-orange, delimited by a pale yellow to yellow-golden prothallus, sometimes inconspicuous, abundantly covered with heaps or more or less cracked crust of isidia, simple or finger-like to branched-coralloid - often forming a thin to thick and fluffy areolate isidiate crust, yellow-orange to orange according to exposition. Apothecia rare, often scattered, to 1 mm diam., disc rounded, flat, orange; proper margin orange, often becoming excluded when old. Ascospores ellipsoid, polarilocular, 11-15 x 5-7 µm, septum 1-4 µm wide, to about 1/4 of the length of the ascospore. Photobiont : trebouxioide. All parts K + purple. On well lit siliceous rocks but in protected zones notably in horizontal fissures or vertical walls.
N.B. On the same site it is possible to find specimen entirely covered with isidia, hiding the thallus, and other specimen with very few isidia leaving a thallus reduced to a mere yellow-orange rough crust. Very difficult to distinguish from Caloplaca britannica which has minute radiating lobes, globular isidia, and is paler yellow and growing within the Verrucaria (Hydropunctaria) maura zone and from Caloplaca citrina ss. auct. brit. which has granular soredia, more yellow-lemon on less acid and more humid rocks.