in Arup & al., Nord. J. Bot., 31: 36, 2013. Basionym: Caloplaca saxifragarum Poelt - Feddes Rep., 58: 176, 1955.
Synonyms: Callopisma luteoalbum f. microcarpum (Anzi) Arnold; Caloplaca pyracea var. microcarpa (Anzi) Dalla Torre & Sarnth.; Caloplaca schoeferi Poelt; Placodium luteoalbum f. microcarpum Anzi
Distribution: N - Frl, Ven (Nascimbene 2002, 2008c), TAA (Nascimbene & al. 2006, 2022, Nascimbene 2008b), Lomb (Dalle Vedove & al. 2004), Piem (Isocrono & al. 2004), VA (Piervittori & al. 2004). C - Marc (Nimis & Tretiach 1999), Abr (Nimis & Tretiach 1999, Di Nuzzo & al. 2021, Vallese & al. 2022), Umb (Ravera & Di Toma 2003, Ravera & al. 2006), Abr (Gheza & al. 2021). S - Cal (Ravera & al. 2016).
Description: Thallus crustose, usually thin and continuous, sometimes almost endosubsratic, pale grey to almost white, very rarely yellowish white, forming 0.5-2 cm wide patches. Cortex usually poorly developed, of an amorphous layer or indistinctly paraplectenchymatous; medulla poorly developed. Apothecia frequent, zeorine, scattered to crowded, adnate to sessile, 0.3-1 mm across, with a flat to slightly convex, bright orange to yellow-orange disc, a thick, yellow-orange (often paler than disc) proper margin, and a poorly developed, greyish to yellowish grey thalline margin. Proper exciple of irregularly radiating, thick-walled hyphae; epithecium orange, granular, K+ red; hymenium colourless, 70-90(-100) μm high, amyloid; paraphyses (1-)2-2.5 μm thick at base, the apical cells (2-)4–6 μm wide; hypothecium colourless, sometimes inspersed 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 to broadly ellipsoid, (8.5-)10-15 x (4.5-)6-8(-10) μm, the equatorial thickening (“septum”) (3-)4-5.5(-7.5) μm, ratio of septum/spore length (0.26-)0.30-0.45(-0.50). Photobiont chlorococcoid. Spot tests: thallus K-, C-, KC-, P-; apothecia K+ red. Chemistry: thallus without lichen substances; apothecia with parietin (major), fallacinal, emodin, teloschistin and parietinic acid (minor), corresponding with chemosyndrome A of Søchting (1997).
Note: a circumpolar, arctic-alpine lichen found on plant debris (especially on dead leaves of Saxifraga, Dryas and Carex firma), and on muribund bryophytes in open habitats over calcareous or dolomitic substrata, most common above treeline and reaching the highest mountains of southern Italy. On the synonymisation of Caloplaca schoeferi see Vondrák & al. (2016).
Growth form: Crustose
Substrata: soil, terricolous mosses, and plant debris