Synonyms: Caloplaca holocarpa auct. ital. p.p.; Caloplaca lithophila auct. non H. Magn.; Caloplaca luteoalba var. saxicola (Hepp) H. Olivier; Flavoplaca oasis A. Massal.) Arup, Frödén & Søchting f. lithophila auct.
Description: Thallus crustose, episubstratic or almost absent, forming 0.2-2(-2.5) cm wide patches, up to 0.2(-0.3) mm thick, of scattered to contiguous, 0.1-1 mm wide, pale yellow to (usually) grey areoles (often blackened due to cyanobacteria). Cortex poorly developed, of an amorphous layer or indistinctly paraplectenchymatous; medulla inconspicuous. Apothecia zeorine/biatorine, frequent, scattered to crowded, immersed to adnate, 0.2-0.4(-0.7) mm across, with a flat to slightly convex, orange to brownish orange disc often overgrown by black cyanobacteria, and a thin, sometimes finally excluded proper margin. Proper exciple of irregularly radiating, thick-walled hyphae; epithecium orange, granular, K+ red; hymenium colourless (50-)65-75 μm high; paraphyses usually simple, sometimes sparingly branched in upper part, 1.5–2.5 μm thick at mid-level, the apical cells 4-6 μm wide; hypothecium colourless. Asci 8-spored, cylindrical-clavate, Teloschistes-type. Ascospores 2-celled, polarilocular, hyaline, ellipsoid, (8-)9.5-13(-14) x 4-7 μm, the equatorial thickening (“septum”) (2.5-)3-4.5 μm. Pycnidia rare immersed, orange. Photobiont: chlorococcoid. Spot tests: apothecia K+ red, C-, KC-, P-. Chemistry: apothecia with parietin (major), fallacinal, emodin, teloschistin and parietinic acid (minor), corresponding with chemosyndrome A of Søchting (1997).
Note: this lichen, which is quite common on limestone and mortar throughout Italy, has been much misunderstood. Arup (2009) places it within the variation range of F. oasis, but here I follow Roux & coll. (2014) in maintaining it as a separate entry, albeit with a provisional name, because of the very different ecology and life-cycle (it is not parasitic on Bagliettoa-species). Many recent Italian records were under the name Caloplaca holocarpa, or Caloplaca lithophila.