Description: Thallus crustose, very variable, from endosubstratic and poorly evident to episubstratic and finely rimose-areolate, white to pale yellow, often delimited by a thin, black prothalline line. Apothecia biatorine, at first immersed, then sessile, rounded, 0.2-1.3 mm across, with a rusty red to dark orange-red, at first flat, then convex, epruinose disc, and a somewhat paler, smooth, at first well-visible, finally often excluded proper margin. Epithecium brownish orange, K+ red; hymenium colourless, 40-60(-80) µm high; paraphyses simple or forked in upper part, c. 1 µm thick at base, the apical cells (2-)3-4.5 µm wide; hypothecium colourless. 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, ellipsoid, (9-)10-13(-14) x (3-)5-6(-10) µm, the equatorial thickening (“septum”) up to 5 µm. Photobiont chlorococcoid. Spot tests: thallus K- or K+ faintly red; C-, KC-, P-; Apothecia K+ red. Chemistry: thallus without lichen substances or with low amounts of fragilin; apothecia with parietin and emodin (major), and citreorosein, emodinal, fallacinal and parietinic acid (minor).
Note: a Mediterranean species found on compact limestone, locally very abundant in coastal situations, extremely rare far from the coast. The colour of the thallus, based on which several infraspecific taxa were distinguished (see e.g. Roux & coll. 2014); at least one of them is a distinct species.