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. On serpentine or weakly acid metamorphic rocks of the mesic-supralittoral seashores; not found up to now in Brittany, but present in Cornwall and Cape Lizard, suggesting a possible extension to our prospection area in the very western parts of Brittany. N.B. Caloplaca grimmiae is rather similar but without visible thallus and grows on Candelariella vitellina. N.B. Pictures presented here correspond to samples collected in Corsica and Levant Island on vertical walls of rocks subjected to sea spray.