Description: Thallus crustose-placodioid, episubstratic, salmon-coloured to brownish orange, often thinly white pruinose, especially in central part, forming regular, up to 1.8 cm wide rosettes, several thalli often merging to cover larger surfaces. Central part areolate, with flat to convex, 0.3-1.3 mm wide areoles formed from lobe fragmentation; marginal lobes convex, sometimes becoming flat toward the somewhat broader apex, finger-like or strongly branched, always contiguous, 0.3-1.7 mm long. 0.2-1.2 mm wide. Thallus 100-365 μm thick; upper cortex 14-65(-85) μm thick, with an orange, K+ red upper layer layer and a colourless inner layer, scleroplectenchymatous, the upper part with many crystals visible under polarized light; medulla quite lax. Apothecia pseudolecanorine or zeorine, abundant, crowded, 0.2-1.2 mm across, rounded or deformed by mutual compression, usually on areoles and lobe bases. Disk flat to strongly convex, orange to brownish orange, slightly pruinose, smooth; margin in pseudolecanorine apothecia 30-130 μm thick, concolorous with disc; in zeorine apothecia, proper margin 30-50 μm thick and thalline margin 30-130 μm thick, the former slightly lighter than disk, not prominent, the latter pruinose. Epithecium (6-)8-10(-12) μm thick, orange, K+ red; hymenium colourless, 50-80(-95) μm high; paraphyses septate, forked or weakly branched subapically, (1.5-)2-3(-3.5) μm at base, the apical cells (2.5-)3-7(-8.5) μm wide; hypothecium colourless, scleroprosoplectenchymatous. 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, broadly ellipsoid (9-)10.5-13.5(-16) x (4.5-)5.5-7(-8.7) μm, the equatorial thickening (“septum”) (2.5-)3-4.5(-6) μm, > 1/3 of spore length. Photobiont chlorococcoid. Spot tests: thallus and apothecia K+ red, C-, KC-, P-. Chemistry: thallus and apothecia with parietin (major), fallacinal, emodin, teloschistin and parietinic acid (minor), corresponding with chemosyndrome A of Søchting (1997).
Note: this coniophilous and nitrophilous, much misunderstood species, grows mainly on walls and calcareous rocks, also in urban environments (e.g. it is abundant in parts of Venice) and has been frequently called Caloplaca saxicola in the past. It is certainly widespread and common in Italy, and most of the earlier records of C. saxicola refer to this taxon. For further details see Gaya (2009) and Gaya & al. (2011).