Caloplaca fuscoatroides J. Steiner
Thallus crustose relatively thick, very irregular, bordered and cracked to subsquamular, very dark, greyish, dark greyish, blackish, prothallus sometimes present, blackish. Apothecia usually quite numerous, sessile, 0.5-1 mm in diameter, flat disc and the remainder, dark ferruginous red, reddish brown a little orange, dark red, margin clear, not crenate, persistent, concolor or paler. Polarilocular spores, colorless, broadly elliptical, 13-16 x 7-10 µm, with equatorial thickening of 1/3 to 1/2 of the total spore length. Frequent presence of protruding pycnidia with rounded, black apex. Apothecia: K + purple. Maritime and thermophilic species occurring on large siliceous stones, dry stone walls, vertical walls of large rocks in the xeric zone of marine shores. Easy to confuse with Caloplaca crenularia and especially Caloplaca crenularia var. contigua with the paler thallus and at the margin of the crenellated apothecia whose habitat is more extensive and less strictly maritime and also with Caloplaca ceracea very close species (and perhaps conspecific?) but whose habitat is more humid and which does not support not so much the sun and the projections of sea water, and whose apothecia disc is a little greenish in wet weather. N.B. The taxon from the Atlantic coasts is probably different from that described from the Mediterranean coasts.