Pyrrhospora quernea

Thallus thick, blastidiate with granules to ca 0.15 mm diam. arising over the surface of the thallus and breaking down into soredia, even, often indistinctly areolate, yellowish or greenish fawn; prothallus generally present, forming a delimiting black line to 0.25mm wide. Apothecia 0.4–1 (–1.5) mm diam., strongly convex, often irregular in shape, dark reddish brown; true exciple becoming excluded; epithecium interspersed with reddish brown granules, K+ dissolving, purplish (7-chloro-emodin). Ascospores (7–) 8–12 (–14) × (5–) 6–7 (–8) µm. Thallus C+ orange, K–, K/UV(wet)+ bright yellow-green, KC+ orange, Pd– or weakly yellowish, UV± blackish orange (arthothelin and thiophanic acid).

Lecanora expallens has a thinner, finer, sorediate thallus, with the sorediate crust developed lens-shaped soralia not blastidia, which is much more distinctly yellowish green thallus, lacking a fawn tint and is without a distinct black prothallus; its thallus contains usnic as well as thiophaninic acid. Pertusaria flavida can be similar but has at least some distinct isidia and lacks the fawn tints and arthothelin of Pyrrhospora quernea and is UV+ very bright orange. Cliostomum flavidulum is a brighter yellow-green has fine soralia and is C–, K/UV(wet)– and Pd+ orange-red. Lecanora compallens is also C–, K/UV(wet)– but is Pd–.

Rarely parasitised by the small black disks of Lecidella parasitica. These are easily overlooked as immature apothecia of Pyrrhospora quernea, but can be detected by their small size, pure black colour (no trace of reddish pigmentation) and the disks remaining flat.