Description: Thallus crustose, endosubstratic or thinly episubstratic in the sorediate parts, whitish to pale yellow-green, forming extensive sorediate patches, without a distinct prothallus. Soralia irregular in size and form, bursting through the uppermost cell layers of the bark, at first discrete and punctiform, later often confluent and forming diffuse patches. Soredia variable in form and size, 20-100 μm in diam. Apothecia biatorine, rare, up to 0.6 mm across, with a pale yellow (turning orange brown in the herbarium), flat to convex disc and a paler, more or less prominent, thin, proper margin. Proper exciple of radially arranged hyphae, faintly purplish in outer part, colourless and densely granular within, the granules soluble in K; epithecium colourless or pale yellow, often with granules; hymenium colourless, I+ blue; paraphyses mostly simple, with more or less clavate apices; hypothecium colourless. Asci 8-spored, cylindrical-clavate, the tholus with a conical, blunt, a sometimes indistinct ocular chamber and a distinctly conical axial body, the remainder of tholus I+ dark blue, darkest around the axial body. Ascospores 1-septate. hyaline, narrowly ellipsoid, straight or slightly curved, 10-13 x 2-2.5 µm. Pycnidia always present, black, up to 0.4(-0.6) mm in diam., irregularly rounded, with a brown, K-, N+ reddish-violet wall. Conidia subglobose to drop-shaped, (2-)2.5-3 x 1.5-2 μm. Photobiont chlorococcoid. Spot tests: thallus K+ yellow, C-, KC+ yellow, P-. Chemistry: thallus with atranorin and caperatic acid, apothecia with usnic acid.
Note: a generally very rare species found on the bark of conifers in humid old-growth forests, usually in sites protected from rain; widespread in the Holarctic region, with a few records from the Alps outside the Italian territory. To be looked for in the Alps.
Growth form: Crustose
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly asexual, by soredia, or soredia-like structures (e.g. blastidia)