Description: Thallus foliose, broad-lobed, loosely attached, forming wide-spreading, usually orbicular patches 6-20(-40) cm across. Lobes broad and rotund, (0.5-)1-1.5(-2) cm wide, with raised, wavy margins, greenish grey (sometimes tinged brown), with punctiform pseudocyphellae on upper surface, which are rather small and usually not raised, often concentrated in the submarginal parts of lobes; pseudocyphellae on the lower surface not developed, or appearing as very small white dots. Soralia primarily marginal, elongated, usually smooth, with fine to rather coarse soredia. Lower surface black, rather regularly ridged, with scattered, simple, black rhizines and a brown, rhizine-free zone along the margin. Upper and lower cortices prosoplectenchymatous, with a non-pored epicortex, of densely agglutinated hyphae with tiny lumina; medulla white, with isolichenan, I-. Apothecia very rare, lecanorine. Asci 8-spored, Lecanora-type. Ascospores 1-celled, hyaline, ellipsoid, 12-15 x 7-10 µm. Pycnidia: unknown. Photobiont chlorococcoid. Spot tests: cortex K+ (weakly) yellow, C-, KC-, P-; medulla and soralia K+ yellow, C+ strongly blood-red, KC+ reddish, P-, UV-. Chemistry: cortex with atranorin and chloroatranorin (in lower amounts than in soralia); soralia (and medulla) with atranorin, olivetoric acid, anziaic acid, and 4-O-demethylmicrophyllinic acid, sometimes with a fatty acid.
Note: a species with the olivetoric acid syndrome, found on bark of broad-leaved trees and on epiphytic, more rarely silicicolous mosses in humid, old forests, locally still locally abundant in montane Abies-Fagus forests, especially in the eastern Alps. Here the species, which is certainly widespread in Italy, is still treated in a broad sense: several records before 2007 could refer to the other species of the complex. The species was included in the Italian red list of epiphytic lichens as “Near-threatened” (Nascimbene & al. 2013c).
Growth form: Foliose, broad lobed
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly asexual, by soredia, or soredia-like structures (e.g. blastidia)
Most common in areas with a humid-warm climate (e.g. most of Tyrrenian Italy)