Squamules: up to 4 mm diam., at first round, saucer-like, entire, slightly convex in the center, later deeply divided into folded, bullate or even tube-like rolled lobes, isodiametrical or slightly elongated, attached to the substrate in the center, free at the periphery, scattered to contiguous and aggregated in rosettes or in bigger compact patches up to 7 cm in diam. and then partly overlapping. Upper side: medium brown to creamy colored, sometimes reddish or yellowish olive-brown, slightly glossy to dull, with white, continuous, even, thick pruina which may occasionally be disintegrated or absent in shaded thallus portions, long remaining smooth, later moderately cracked in convex thallus portions. Margin: concolorous with upper side, becoming slightly down-turned, entire when young, later deeply lobed, not crenulate. Underside: whitish near margin, inwards soon ochraceous brown, with rhizohyphae at centre of squamule. Upper cortex: 70-80 μm thick (including a thin, c. 10 μm thick epinecral layer), composed of rather thin‑walled hyphae with round to ellipsoid lumina, containing crystals dissolving in K (K-, C+ red; i.e. gyrophoric acid) in the stainable layer and calcium oxalate in the epinecral layer and on the surface of the cortex. Medulla: containing both crystals dissolving in K (K-, C+ red; i.e. gyrophoric acid) and calcium oxalate. Lower cortex: composed of thick‑walled, pale brown, irregularly to mainly periclinally oriented hyphae, lacking crystals. Apothecia: up to 1.5 (-2) mm diam., attached laminally and marginally to the squamules, simple or aggregated in groups of 2-6 or even more, not rarely confluent into composite fruits, strongly convex and immarginate even when young, medium brown, often with a reddish hue, dull to slightly glossy, usually with moderate, white or occasionally yellow pruina (sometimes pruina thick or absent). Ascospores: 14-17 x 7-8 μm. Pycnoconidia: c. 5 x 1 μm. Thallus chemistry: Gyrophoric acid and bourgeanic acid.
The species is morphologically most similar to the North American Psora tuckermanii, but differs in its secondary chemistry and ascospore size: P. tuckermanii is acid deficient and the spores 8-12 x 6-8 μm. Psora tuckermanii is morphologically variable, but the squamules are generally larger when fructifying (up to 6 mm in diameter) and concave to only weakly convex.
Yakutia.
The species grows on calcareous soil over limestone outcrops in open habitats.
Psora tuckermanii.
