Description: Thallus foliose, forming irregular rosettes mostly <4 cm in diam. Lobes bright lemon-yellow to greenish yellow in shade-forms, smooth, dull, dorsiventral, adnate to ascending, (0.5-)1-3(-5) mm wide, with rounded apices and undulate, more or less ascending, sorediate margins. Soredia bright yellow, finely granular. Lower surface concolorous with upper surface or paler, with scattered, brownish white rhizines. Upper and lower cortex paraplectenchymatous; medulla yellow, very loose. Apothecia extremely rare, lecanorine, with a brown disc and a more or less smooth thalline margin. Asci 8-spored, broadly clavate, Lecanora-type. Ascospores 1-celled, colourless, subglobose, c. 5-6 µm in diam. Pycnidia rare, black, pyriform to subspherical, on marginal projections. Conidia bottle-shaped, 6-8 x 1-2 µm. Spot tests: cortex K-, C-, KC+ yellow, P-; medulla K-, C-, KC-, P-, UV+ blackish red. Chemistry: cortex with usnic acid; cortex and medulla with vulpinic and pinastric acids (major), zeorin and unknowns (accessory).
Note: a subarctic-subalpine to boreal-montane, circumpolar species found on basal parts of trunks, especially of conifers, and on twigs with long snow-lie, often associated with Parmeliopsis near treeline; common only in the Alps, much rarer, and mostly confined to Castanea or conifers stands in the Apennines.
Growth form: Foliose, broad lobed
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly asexual, by soredia, or soredia-like structures (e.g. blastidia)