Athallia pyracea

Thallus very thin and sometimes (at least partially) immersed in bark, flat to weakly verruculose, often rimose; the areoles then 50–200 µm diam.; pale greyish to greyish yellow, orange-yellow to orange, rather often with a greyish base colour and yellow to orange scattered spots. Prothallus sometimes visible, thin and grey. Cortex usually poorly developed, composed of an amorphous layer of indistinct isodiametric cells. Apothecia normally present and abundant, scattered to crowded, rarely contiguous, adnate to sessile, round to somewhat irregular, 0.3–1.0 mm diam.; disc flat to slightly convex, orange; thalline margin mostly present but sometimes excluded; exciple (25–) 35–50 (–60) μm thick, slightly raised or level with the disc; epithecium orange, granular-inspersed; hymenium 70–90 (–100) μm thick, colourless; hypothecium (50–)70–100 μm thick, hyaline, sometimes oil-inspersed; paraphyses unbranched or branched above, the upper cells inflated to 4–7 μm diam.; asci 8-spored. Ascospores ellipsoidal to broadly ellipsoidal, (8.5–) 10–15.5 × (4.5–) 5.5–8 (–9) μm, polarilocular, the septum (3.3–) 3.8–5.5 (–6.5) μm thick, mostly 1/3–1/2 the spore length. Yellow parts of thallus and apothecia K+ purple.

Characterised by a greyish thallus that may appear piebald due to islands of yellow pigmentation, and relatively large apothecia with thin thalline margins. May be confused with morphs of Caloplaca ahtii with poorly developed soralia.