Distribution: N - Frl (Obermayer & Mayrhofer 2007), Ven (Nascimbene & al. 2021), TAA (Obermayer & Mayrhofer 2007, Nascimbene 2014, Nascimbene & Marini 2015), Lig (Ravera & al. 2019b). C - Sar (Nascimbene & al. 2021).
Description: Thallus foliose, loosely attached, forming wavy, wide-spreading, usually orbicular patches 6-20(-40) cm across. Lobes broad and rotund, (0.5-)1-1.5(-2) cm wide, with raised margins, greenish grey (sometimes tinged brown), pseudocyphellate; pseudocyphellae on upper surface frequently developing on slightly raised structures, often appearing as accumulation of individuals to form a larger unit, sometimes lacking in the central parts of older thalli, those on the lower surface usually absent (but sometimes sparingly developed). Soralia primarily marginal, often rather irregularly shaped, with coarse soredia [(35-)-40-55 µm diam.]. Medulla white. Lower surface black, wrinked, with scattered, simple, black rhizines and a brown, rhizine-free zone along the margin. 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- or C+ faintly pink/violet, KC+ pale pink of pale reddish brown, P-. Chemistry: cortex with atranorin and chloroatranorin (in lower amounts than in soralia); soralia (and medulla) with atranorin, imbricaric acid (major), perlatolic acid (minor or traces), 4-O-demethylimbricaric acid (minor or traces), anziaic acid (traces), an unidentified fatty acid, sometimes with traces of glomelliferic, loxodellic and divaricatic acid.
Note: a species with the imbricaric acid syndrome (major) and perlatolic acid (minor), found on the bark of broad-leaved trees, more rarely on silicicolous mosses in humid, old, mostly montane forests; probably the most common species of Cetrelia in Italy (see comment on the genus). It is included in the Italian red list of epiphytic lichens as “Data Deficient” (Nascimbene & al. 2013c). See also note on Cetrelia olivetorum.
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)