Description: Thallus crustose, inapparent or consisting of small, thin, scattered, convex, yellow to green-yellow granules, sometimes surrounded by a thin, dark grey to black prothallus. Apothecia frequent, lecanorine, yellow, 0.25-1.2 mm across, with a flat to convex disc and a yellow (often brighter than disc), persistent, smooth to crenulate thalline margin. Proper exciple of strongly gelatinized, thick-walled hyphae with elongated to rectangular cells, forming a distinct stipe penetrating downward through the algal layer; epithecium yellow-brown; hymenium colourless, 60-80 µm tall, amyloid; paraphyses simple or sometimes branched in upper part, cylindrical or weakly swollen apically, with up to 3.5 µm wide tips; hypothecium colourless. Asci 8-spored, clavate, with an apical dome which is I+ blue only in the internal, lower part, interrupted in the centre by a I+ paler blue strip, Candelaria-type. Ascospores 1-celled to 1-septate, hyaline, oblong-ellipsoid, (10-)12-18 x 4-7 µm. Photobiont chlorococcoid. Spot tests: thallus and apothecia K-, C- KC-, P-. Chemistry: calycin, pulvinic acid, pulvinic acid-dilactone and vulpinic acid.
Note: a holarctic, subtropical to arctic-alpine, almost cosmopolitan species found on a wide variety of calciferous substrata, from limestone and dolomite to mortar, asbestos-cement and concrete, exceptionally on eutrophicated and dusty lignum and bark. The species is very polymorphic: further study is needed on some forms above treeline, and on the biology of other forms regularly starting the life-cycle as parasites of crustose lichens.