Thallus discontinuous with scattered to continuous convex areoles or weakly cracked-areolate, to several cm diam, 50-150 µm thick; areoles 0.1–0.5 mm diam, flat to slightly convex or uneven; pale greyish to greyish yellow or yellow. Margin normally thin and indistinct. Prothallus sometimes present, usually thin, white or pale yellow, film-like, occurring at the margin of the thallus or between areoles. Cortex usually poorly developed or indistinctly paraplectenchymatous.
Anamorph: conidiomata pycnidia, rarely observed, immersed, orange. Conidia 3.0–3.2 × ca 1–5 μm, broadly ellipsoidal.
Teleomorph: ascomata apothecia, normally present, sometimes abundant but usually scattered, 0.3–0.5 (–0.6) mm diam, ± sessile, round to irregular. Disc plane to convex, yellow to orange, often dark orange in old apothecia, proper margin (0–)25–50(–75) μm thick, slightly raised or level with disc, concolorous with or paler than the disc, consisting of irregularly radiating, thick-walled hyphae 5–15 × 1.5–6 μm in size; thalline margin usually very inconspicuous and sometimes ± excluded, to 25 μm thick. Epihymenium orange, interspersed with granules; hymenium 50–80 μm thick, hyaline; hypothecium 35–80 μm thick, hyaline. Interascal tissue of paraphyses, simple to branched above, 2– 2.5 μm diam with upper cells to 6 μm diam, rarely if ever with oil-droplets. Asci 45–55 × 10–14 μm, cylindrical, 8-spored. Ascospores (8–) 9–12 (–14) × 4–6 (–7) μm, ellipsoidal, polarilocular, the septum (2.5–) 3.0–4.5 (–5.0) μm wide.
Similar to Athallia holocarpa, but tends to have a better developed thallus with scattered rather than clustered ascomata. The ascospores of A. vitellinula are shorter than those of A. holocarpa, and have thinner septa. Flavoplaca oasis has darker orange ascomata and occurs on limestone rocks or mortar/concrete.
In GB&I, reported from Scotland (W Ross) and Wales (Cardiganshire, Radnorshire). Widely distributed in Scandinavia, especially in more northerly parts. Many older records belong to other species, especially Flavoplaca oasis.
In GB&I, found on well-drained siliceous rock, on vertical faces and often under overhangs. Elsehwere, also occasionally found on calcareous rock and even on wood.