Synonyms: Biatora caesiorufa auct. p.p. non (Wibel) Fr.; Caloplaca caesiorufa auct. p.p. non (Wibel) Flagey; Caloplaca scotoplaca (Nyl.) H. Magn.
Distribution: N - TAA, Lomb, Piem, Emil (Valcuvia & Delucchi 2001). C - Tosc, Laz, Sar (Rizzi & al. 2011). S - Camp, Si.
Description: Thallus crustose, episubstratic, thin, continuous to rimose-areolate, ash-grey to dark grey. Areoles 0.2-0.4 mm wide, 0.1-0.2 mm thick, irregular, plane to uneven, separated by very thin, often indistinct cracks. Apothecia adpressed, circular to angular by mutual compression, 0.2-0.4 mm across, with a flat to slightly convex, bright to dark rust-red, finally sometimes blackening disc, and a thin, mostly persistent, first paler, then concolorous, rarely excluded margin. Exciple brownish yellow in outer part, colourless within; epithecium brownish yellow, interspersed with orange-yellow crystals of anthraquinones reacting K+ red; hymenium 60-70 μm high, colourless or yellowish in upper part, amyloid; paraphyses simple or sparingly branched in upper part, c. 1.7 μm thick at base, the uppermost cells swollen and 4-5 μm wide; hypothecium 20-50 μm thick, colourless to greyish, I+ dark blue. Asci 8-spored, clavate, Teloschistes-type. Ascospores 1-septate, polarilocular, hyaline, narrowly ellipsoid, 10-13 x 4-8 μm, the septum (2-)3-5 μm thick. Photobiont chlorococcoid. Spot tests: thallus K- or K+ weakly violet in section, C- or C+ violet, KC-, P-; disc of apothecia K+ red. Chemistry: thallus with the Sedifolia-grey pigment; disc of apothecia with different anthraquinones.
Note: at least in southern Europe this lichen of basic, hard siliceous rocks has been much misunderstood; several earlier Italian records, especially those from outside the Alps, need confirmation, as well as those from Sardegna (see Nimis & Poelt 1987: 74).