Sanguinodiscus aractinus (Fr.) V. Frolov & Vondrak = Caloplaca aractina (Fr.) Häyren

    Thallus crustose, areolate, lead-grey to blackish, smooth to rimose, uneven, bounded by a black prothallus. Apothecia to 1 mm diam., first immersed, soon becoming emergent to sessile, disc flat, yellow-orange, brown-orange, grey thalline margin persistent. Ascospores polarilocular,  broadly ellipsoid, polarilocular, septum 3-5 µm wide, c. 1/3 of the length of the ascospore, 10-13 (15) x 5-8 µm. Photobiont : trebouxioid. Apothecia disc K+ purple hardly visible, disc K+ purple. Species found on serpentines or low acid metamorphic rocks of the mesic supralittoral seashores of British Cornwall and Cape Lizard, very rare at the tip of Brittany, but common on the vertical walls of coastal rocks subjected to seawater splashes and the spray of the Mediterranean coasts and particularly in Corsica and Sardinia.

N.B. Caloplaca grimmiae is rather similar but without visible thallus and grows on Candelariella vitellina.