Synonyms: Callopisma aurantiacum var. microsporum Arnold; Caloplaca aurantiaca var. microspora (Arnold) Dalla Torre & Sarnth.
Distribution: N - Frl, TAA, Piem (Matteucci & al. 2013, Favero-Longo & al. 2015), VA (Favero-Longo & al. 2006, Isocrono & al. 2008, Favero-Longo & Piervittori 2009). C - Abr (Nimis & Tretiach 1999, Gheza & al. 2021).
Description: Thallus crustose, at first perhaps facultatively parasitic,but soon becoming autotrophic, ochraceous yellow to yellow-orange, finely areolate or consisting of a few dispersed granules, when well-developed forming small patches to 2 cm wide. Areoles indistinct or rounded-angular, separated by deep cracks, flat to slightly convex, 0.2-0.5 mm wide, subparaplectenchymatous throughout, filled by algae which almost reach the upper surface. Apothecia zeorine, usually 1 per areole, broadly adnate to slightly constricted at base, 0.2-0.8 mm across, with a flat to slightly convex, orange disc, and a paler, yellow-orange, persistent margin. Exciple of slightly radiating hyphae; epithecium orange-brown, granular, K+ red; hymenium colourless, 60-80 µm high; paraphyses capitate, the apical cells to 6.5 µm wide, covered by epipsamma granules. Asci 8-spored, clavate Teloschistes-type. Ascospores 1-septate, polarilocular, hyaline, narrowly ellipsoid to spindle-shaped, 7-11(-13) x 3-4.5 µm, the septum often poorly developed, 1(-2) µm thick. Photobiont chlorococcoid. Spot tests: thallus and apothecia K+ red, C-, KC-, P-. Chemistry: thallus and apothecia with unidentified anthraquinones.
Note: a probably arctic-alpine species typical of Alpine peaks, found on limestone and dolomite in exposed habitats, often starting the life-cycle on other lichens; probably widespread throughout the Alps. According to Vondrák (in litt.) the few available sequences suggest that it could be a limestone variant of the silicicolous, arctic-alpine Amundsenia approximata (Lynge) Søchting, Arup & Frödén.