Caloplaca variabilis (Pers.) Müll. Arg.

    Thallus crustose, usually circular, rather thick, rugose, cracked to areolate, dark grey, dark grey-brown, dull brownish, margin characteristically paler, dull whitish to pale grey, prothallus sometimes dark grey. Apothecia scarce to numerous and in that case distorted owing to compression, sessile, 0.5-1 mm diam., disc smooth, flat to slightly concave, dark brownish to blackish, tinged grey-blue because of a thick grey-blue persistent pruine, exciple entire, occasionally wavy, whitish. Ascospores ellipsoid, polarilocular, 1-septate, 14-18 x 7-9 µm, septum  3-5 µm. Thallus and apothecia K- or K+/- purplish-blue. Very rare in our prospection area, mainly found on dull and dusty calcareous rocks in fallow and waste lands. See Caloplaca alociza which is more thermophile, with a very thin thallus, smaller and not sessile apothecia, and less blue discs.