Thallus ± completely covered by isidia, where exposed flat to slightly scurfy-granular, concolorous with isidia or slightly paler. Isidia 50–90(–110) μm diam, light beige to orange, sometimes dark orange or brown, occasionally grey or green, normally branched and forming a delicate coral-like structure, often layered and forming a cracked-areolate crust.
Anamorph: conidiomata pycnidia, rare but abundant when they occur, immersed, ostiole red and slightly raised. Conidia 3.0–5.0 × 0.8–2.0 μm, bacilliform to narrowly ellipsoidal.
Teleomorph: ascomata apothecia, adnate to sessile, round to very irregular or lobate (the irregularity increasing with age), younger apothecia orange to light red, darkening to a more ferruginous red with age Disc strongly concave to convex, older apothecia sometimes increasingly convex, the margin slightly raised or level with the disc, 60–85 μm thick, consisting of ± radiating, elongate cells 4–10 (–15) × 2.5–4 μm in size, algae sometimes occurring at the base. Epihymenium orange, granular. Hymenium (80–)85– 100(–105) μm in height, hyaline. Hypothecium (50–) 60–100(–110) μm in height, frequently brown-pigmented, often with oil droplets. Interascal tissue of paraphyses, simple or branched above, 1– 2.5 μm diam, the upper cells sometimes slightly widened. Asci 50–70 × 10–16 μm, clavate, 8-spored. Ascospores (10–) 11.5–14 (–15) × (4–) 6–8 (–9) μm, polarilocular, with a ± median septum (3–) 3.5–4 (–5) μm thick.
Chemistry: Thallus K+ purple red and C+ light red, (K− and C− on specimens without orange colour).
Similar to Blastenia (Caloplaca) herbidella, but with beige to orange rather than grey isidia. It is rarely fertile, in contrast to B. herbidella that almost always has apothecia.
In GB&I, only known from England (Westmorland). Widely distributed in Europe, from southern Scandinavia to Greece, also from Tunisia and Syria.
In GB&I, on bark of ancient Quercus in old deer park. It prefers older deciduous trees with rough bark, such as Quercus, Ulmus and Fraxinus.