Description: Thallus crustose, episubstratic, minutely warted-areolate, the areoles up to 0.1 mm wide, fragile, pale green to green brown, soon dissolving into bright green, 0.1-0.3 mm wide, punctiform and discrete to finally confluent soralia with farinose, 12-20 µm wide soredia, the exterior soredial hyphae with brown to grey-brown walls. Apothecia rare, 0.2-0.4 mm across, with a flat to convex, grey to dark brown, epruinose disc, an ecorticate, sorediate, finally often excluded thalline margin, and sometimes a thin, paler parathecial ring. Proper exciple 12-14 µm wide laterally, up to 33 µm wide in upper part, of coherent, colourless hyphae (except those of the upper edge, which have brown-capped cells); epithecium almost colourless to brown, K-, N-; hymenium colourless, 35-50 µm high, I+ blue; paraphyses coherent, mostly simple, 1.5-2 µm thick at mid-level, the apical cells up to 3 µm wide, with a dark cap; hypothecium colourless. Asci 8-spored, clavate to subcylindrical, with a K/I+ blue outer coat and a K/I+ uniformly blue apical dome, Catillaria-type. Ascospores 1-septate, hyaline, fusiform to clavate-fusiform, often slightly curved, with one cell slightly wider than the other, 12-17(-20) x (4-)5-6 µm, including the gelatinous perispore, the actual spore width 3.5-4.5 µm. Photobiont chlorococcoid, the cells 9-12 µm wide. Spot tests: thallus and soralia K-, C-, KC-, P+ rapidly orange-red, UV-. Chemistry: argopsin.
Note: on slightly eutrophic bark of deciduous trees (mainly Salix) often near rivers and lakes; most frequent in Western Europe, with a few records from the Eastern Alps, but perhaps not always recognised elsewhere.
Growth form: Crustose
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly asexual, by soredia, or soredia-like structures (e.g. blastidia)