in Arup & al., Nord. J. Bot., 31: 38, 2013. Basionym: Caloplaca arnoldiiconfusa Gaya & Nav.-Ros. in Gaya - Bibl. Lichenol., 101: 54, 2009.
Synonyms: Caloplaca arnoldii auct.ital. p.max.p.
Distribution: N - Frl, Ven (Nascimbene & Caniglia 2000, 2003c, Nascimbene 2008c), TAA (Nascimbene & al. 2006, 2022, Nascimbene 2008b), Piem (TSB 33080). C - Umb (Ravera & al. 2011), Sar (ASU 235739). S - Si (Gaya 2009).
Description: Thallus crustose-placodioid, episubstratic, forming well-delimited, 5-11 mm wide rosettes, deep reddish-orange to almost red, mostly epruinose, the central parts often becoming necrotic and whitish. Areoles located in thallus center, polygonal or irregular, relatively flat, 0.4-1 mm in diam., covered with apothecia; marginal lobes deeply divided, convex, rarely slightly flattened toward tips, contiguous to rarely imbricate, 0.1-0.9(-1.5) mm long and 0.1-0.6(-0.9) mm wide at tips. Upper cortex thin, with a yellowish-orange external part and a hyaline inner part, scleroplectenchymatous, with scarce amounts of superficial crystals visible under polarized light; algal layer more or less continuous; medulla white, lax. Apothecia pseudolecanorine, 0.1-0.6(-0.8) mm across, dispersed or grouped on the areoles or lobe-bases, usually rounded or somewhat distorted, with a flat to convex, orange- brown to dull red, epruinose disc and a slightly paler, thin margin. Exciple of radially arranged hyphae, scleroplectenchymatous; epithecium brownish-orange, K+ red; hymenium and hypothecium colourless; paraphyses septate, sparsely branched in upper part, 1.5-3(-3.5) µm wide at base, the apical cell swollen, up to 7(-8.5) µm wide. Asci 8-spored, 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, mostly broadly ellipsoid, (8.5-)10-13(-16) x (3.8-)5-6.5(-7.5) µm, the equatorial thickening (“septum”) (2.5-)3-4(-5) µm. Photobiont chlorococcoid. Spot tests: thallus and apothecia K+ red, C-, KC-, P-. Chemistry: thallus and apothecia with parietin, fallacinal, emodin, and teloschistin.
Note: in the past this species was confused with C. arnoldii, which substitutes in upland areas, on vertical to underhanging surfaces of calcareous and dolomitic rocks. For further details see Gaya (2009) and Gaya & al. (2001).