in Frolov & al., J. Syst. Evol. 59, 3: 468, 2020. Basionym: Blastenia percrocata Arnold - Flora, 67: 309, 1884.
Synonyms: Callopisma percrocatum (Arnold) Jatta; Caloplaca percrocata (Arnold) J. Steiner
Distribution: N - Ven (Frolov & al. 2020), TAA (Vondrák 2008, Vondrák & al. 2008, Nascimbene & al. 2022), Piem (TSB 34342). Lig. C - Tosc, Sar.
Description: Thallus crustose, episubstratic, areolate, whitish grey to dark grey, often with a bluish or brownish tinge, well-delimited, sometimes with a thin, dark grey prothallus, the areoles irregular, uneven, flat to convex, up to 3 mm in diam. Cortex paraplectenchymatous, 15-35 µm thick, obscured by colorless crystals insoluble in K and soluble in N, K– or K+ faintly violet, N+ faintly violet; medulla with many crystals. Apothecia zeorine, often in groups, 0.4-1.5 mm across, angular to flexuose, at first semi-immersed but son becoming sessile, with a flat, brownish orange to brownish red disc contrasting with a paler, yellowish orange, thick, raised proper margin; thalline margin pale yellow, soon excluded and finally poorly visible. Thalline exciple ecorticate in lower part, or with an indistinct, up to 20 µm thick cortex; proper exciple of radiating hyphae; epithecium orange-brown K+ red, C+ purple in section; hymenium colourless 90-120 µm high; paraphyses sparingly branched in upper part, the apical cells up to 5(-6.5) µm wide; hypothecium colourless, with oil droplets. Asci 8-spored, cylindrical-clavate, functionally unitunicate, apically thickened with a broad internal beak, the inner part of apex and external cap I+ blue, Teloschistes-type. Ascospores 2-celled, polarilocular, hyaline, ellipsoid, 14-18(-20) x 6-10(-12) µm, the equatorial thickening (“septum”) 3-6 µm (c. 1/3 of spore length). Pycnidia grey in upper part. Conidia ellipsoid, 2.5-4 x 1.1.5 µm. Photobiont chlorococcoid. Spot tests: thallus K- or K+ violet, C- or C+ violet, KC-, P-; apothecia K+ red, C+ purple. Chemistry: thallus with the sedifolia-grey pigment and chloroemodin; apothecia with chlorinated anthraquinones.
Note: on base-rich and lime-containing siliceous rocks above treeline. The identity of Mediterranean samples (e.g. those from Sardegna) is dubious, and all records from southern Italy reported by Nimis (1993: 180) are not accepted here.