Caloplaca marina (Wedd.) Zahlbr.
Thallus crustose, usually growing in rounded patches up to 5 cm max. length; consists of minute lobules or granular areolate crust, yellow-orange to deep orange; margin not well delimited occasionally indistinctly lobate (small short lobes), paler or whitish prothallus present; often fragmented and poorly developed and then limited to 1 or 2 apothecia and some granules associated to black cyanobacteria (notably on exposed soft rocks), see: Caloplaca marina forme avec cyanobactéries. Apothecia usually very numerous, to 1 mm diam., disc flat at first, later subconvex, bright orange; thalline margin swollen becoming narrower when old, concolorous with the thallus or more yellow. Ascospores ellipsoid, polarilocular, 11-15 x 5-8 µm, septum 3-5 µm wide, about 1/3 of the length of the ascospore. Photobiont : trebouxioide. All parts K+ purple. Very common species on sunny, siliceous and calcareous coastal rocks, in the mesic-supralittoral zone or black belt but also sometimes within the upperpart of the littoral zone; thallus highly variable according to exposition, variation from well conformed and coloured to shrivelled and black due to cyanobacteria, but even in that case apothecia are still easily identified (see pictures). Easy to distinguish from far by its bright colours amongst other species. Occasionally mixed with Caloplaca thallincola which is distinct by its thallus, lobate and well developed as a regular wheel and by its brither colours. Not to confuse with Caloplaca maritima growing in the upper part of the C. marina distribution zone, with less bright colours, no delimited thallus margin, never black (no cyanobacteria) and apothecia disc never orange but brownish wax-yellow.*