Description: Thallus foliose, closely attached, forming regular, up to 7(-10) cm wide, orbicular rosettes. Lobes 3-5(-7) mm wide, yellow-green, with farinose soredia in laminal, convex, often elongated soralia. Lower surface black centrally, brown peripherally, with simple rhizines. Upper cortex of tightly packed, anticlinally oriented hyphae, with a thin pored epicortex, the cell walls with isolichenan; medulla white; algal layer continuous; lower cortex paraplectenchymatous. Apothecia very rare, lecanorine, with a brown, imperforate disc and a sorediate margin. Epithecium brownish; hymenium and hypothecium colourless. Asci 8-spored, clavate, the K/I+ blue tholus penetrated by a faintly amyloid apical cushion with parallel or diverging flanks, the wall K/I-, surrounded by a K/I+ blue outer layer, Lecanora-type. Ascospores 1-celled, hyaline, ellipsoid, 17-18 x 7-8 µm. Pycnidia laminal, immersed, black. Conidia spindle-shaped. Photobiont chlorococcoid. Spot tests: upper cortex K-, C-, KC-, P-; medulla K+ yellow then red, C-, KC+ red, P+ orange, UV-. Chemistry: upper cortex with usnic acid; medulla with salazinic acid.
Note: a mild-temperate lichen found on broad-leaved, more rarely coniferous trees, with optimum in areas with a warm-humid climate, usually below the montane belt. Some coastal saxicolous collections (TSB) are worthy of further study.
Growth form: Foliose, broad lobed
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly asexual, by soredia, or soredia-like structures (e.g. blastidia)