Description: Thallus crustose, episubstratic, areolate, greenish grey to yellowish grey, delimited by a thin, black prothallus, forming several cm wide patches. Cortex paraplectenchymatous, 30-40 µm thick, overlain with an epinecral layer which is particularly thick in the apical parts of isidia; algal layer 40-70 µm thick; medulla white, rather lax, I-. Areoles angular-acute, up to 1 mm wide, completely covered in 1-2 mm tall, papilliform, terete, up to 1 mm wide, often branched, apically widened and flattened isidia with minutely verrucolose and often darker apices, forming distinct glomerules. Apothecia very rare, aspicilioid, 0.3-0.7 mm across, round to irregular in outline, with a black, epruinose disc and a thin thalline margin. Epithecium grey-green to olive-brown, N+ emerald green; hymenium colourless, I+ persistently blue; paraphyses not or slightly branched and anastomosing; hypothecium colourless, not subtended by an algal layer. Asci 8-spored, clavate, the thin outer coat K/I+ blue, the wall and apical dome K/I-. Ascospores 1-celled, hyaline, ellipsoid, 16-19 x 6-12 μm . Pycnidia black, immersed in the thallus. Conidia hyaline, thread-like, 13-19 x 0.7-1 µm. Photobiont chlorococcoid. Spot tests: cortex and medulla K-, C-, KC-, P-. Chemistry: without lichen substances.
Note: a rarely-collected lichen found on siliceous boulders along streams, mostly above treeline, described from the Central Alps; probably overlooked being often sterile with coarse, partly branched, apically flattened isidia; to be looked for also in the Italian Alps.
Growth form: Crustose
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly asexual, by isidia, or isidia-like structures (e.g. schizidia)