Thallus erect, foliose, brittle, golden yellow, on calcareous soils; branching irregular with narrow lobes to 3-4 mm broad, tips somewhat dentate; upper side smooth to slightly sul-cate; underside smooth, of same color as above; medulla yellow, lacking rhizinae. Cortex very irregular in thickness, varying from 8-37 μ in section even in same thallus, prosoplectenchymatous but with a few paraplectenchymatous groups of cells here and there; medulla yellow, very loose, of irregular shaped hyphae with much pigmentary material over them and with much crystaline mineral inclusions between, about 75 μ thick, the hyphae to about 7 μ. Apothecia not seen.

Growing on calcareous soils and between calcareous gravels, this is a circumpolar arctic-alpine species originally described from Kamtchatka. In North America it has been collected south to the Gaspe Peninsula in the east and to New Mexico in the west (Egan 1971). It has apparently not yet been collected in Greenland.

The exceedingly loose medulla and the thinness of the cortex in spots probably contribute to the brittleness of this species, a characteristic quite unlike the toughness of C. juniperina with which it has often been associated. Arctic reports of C. juniperina usually refer to this species.

Global occurrence: Eurasia – Asia Extratropical | Eurasia – Europe | Americas – North America (incl Mexico) | Arctic.  Substrate: wood – dead, living | bark, cork, plant surface – trunks, branches, twigs.  Life habit: lichenized (mutualistic with algal photobionts).  Thallus: foliose (foliaceous), leaf-like; thallus: continuous, diffuse, effuse; [th] upper surface: green(ish) | yellow(ish) (if dull: buff) | yellow(ish) grey; [th marginal and upper surface] specific structures: absent; [th] morphol substructures (eg areoles, lobes, branches) width [mm]: (low) 1.0 (high) 5.0; [th] lower surface: yellow(ish) (if dull: buff) | brown(ish) white; [th lower surface] specific structures: present; [th lower surface] rhizines, rhizoid structures: present; [th lower surface] rhizines, rhizinoid structures: squarrosely branched, squarrose.  Ascomata: absent | present; ascoma: apothecial, apothecioid – hymenial; ascoma [mm]: (low) 2.0 (high) 6.0; ascoma: sessile, superficial; [ascm, if apoth] disc, mazaedium: red(dish) brown (if pale: orange brown); [ascm, if apoth] margin surface; [if perith] periostiolar area, ostiole, involucrellum: green(ish) | yellow(ish) (if dull: buff) | yellow(ish) grey; [ascm, if apoth] margin excipular photobionts: present; [ascm, if apoth] subhymenial layers, hypothecium; [if perith] basal excipulum: hyaline, colourless; [ascm] paraphyses/-oids: present; [ascm] epihymenium, epithecium: brown(ish) (if pale: fawn, tan; if mid: cinnamon) | red(dish) brown (pale: orange brown).  Asci: lecanoralean; [asc] tholus: thickened; [asc] tholus amyloidity (iodine reaction): present; [asc] tholus amyloidity pattern: amyloid with widening axial body towards the apex (= Lecanora-, Parmelia-, Rinodina-types etc).  Ascospores: (median) 8.0; [asp] length [µm]: (low) 4.0 (high) 10.0; [asp] width [µm]: (low) 2.5 (high) 6.0; [asp] septa: absent – spore lumen unilocular, monolocular; [asp] pigmentation: hyaline, colourless; [asp] perispore, epispore: not apparent.  Conidiomata: absent | present.  Conidia: fusiform; [co] length [µm]: (low) 3.5 (high) 8.0.  Secondary metabolites: present, pinastric acid | usnic acid | vulpinic acid.  Primary photobiont: chlorophytaceous – trebouxiaceous, chlorococcoid.  Secondary photobionts (eg in cephalodia): absent.