Description: Thallus foliose to subfruticose, heteromerous, dorsiventral, at first loosely adnate, but often soon ascending or pendent, forming up to 10(-15)cm broad, irregular rosettes or irregularly spreading, the lobes swollen, hollow inside, 0.5-2(-3) mm wide, elongate, slender, irregularly branching, separate to imbricate, with small, marginal secondary lobules. Soredia terminal, at first labriform, then becoming strongly lacerate. Upper surface smooth to weakly rugose, whitish, greenish grey or sometimes partially brown, often with a black border. Lower surface black to brownish black, sparsely perforate near tips and at the branching points, erhizinate, often visible from above along lobe margins. Upper cortex of tightly packed, more or less anticlinally oriented hyphae, the cell walls with Cetraria-type lichenan; medulla soon becoming hollow, lining the cavity inside the lobes; lower cortex dark, paraplectenchymatous. Apothecia rare, lecanorine, mainly laminal, brought by hollow stipes, 6-8(10) mm across, with a brown disc. Epithecium brown; hymenium and hypothecium colourless. Asci 8-spored, clavate, Lecanora-type. Ascospores 1-celled, hyaline, broadly ellipsoid, 4.5-7 x 4-5.5 μm. Pycnidia frequent, laminal, black, often in clusters. Conidia narrowly cylindrical to weakly bifusiform, 4.5-6.5 x c. 1 μm. Photobiont chlorococcoid. Spot tests: upper cortex K+ yellow, C-, KC-. P-; medulla K-, C-, KC+ orange-red, P-. Chemistry: upper cortex with atranorin; medulla with physodic acid, 3-hydroxyphysodic acid (both major), and vittatolic acid (minor/accessory.
Note: a circumboreal-montane lichen found on acid bark, often on basal parts of trunks, on acid soil and overgrowing muribund bryophytes, probably restricted to the Alps in Italy. It is included in the Italian red list of epiphytic lichens as “Vulnerable” (Nascimbene & al. 2013c).
Growth form: Foliose, narrow lobed
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly asexual, by soredia, or soredia-like structures (e.g. blastidia)