Squamules: up to 5 mm diam., more or less isodiametrical, adnate, scattered to contiguous or rarely somewhat imbricate. Upper side: medium brown, dull to shiny, epruinose or partly white pruinose, with a few fissures; margin: white, usually ascending, entire or becoming lobate; underside: pale brown. Upper cortex: 70-130 μm thick, composed of rather thin-walled hyphae with round or ellipsoid to angular lumina, sometimes containing calcium oxalate. Medulla: containing norstictic acid and calcium oxalate. Lower cortex: poorly developed or absent. Apothecia: up to 1.2 mm diam., attached laminally to the squamules, usually simple, strongly convex and immarginate even when young, black, dull, frequently partly white pruinose. Ascospores: 9-13 x 5-7 μm. Pycnoconidia: 5-7 x 1 μm. Thallus chemistry: norstictic acid.
The species may mainly be confused with some terricolous forms of P. himalayana and P. tenuifolia, see these species for discussion.
Asia, Europe, northern Africa, and North America.
On calciferous soil or in crevices of rock in open habitats.
Psora himalayana, Psora tenuifolia.