Description: Thallus foliose, broad-lobed, potentially >40 cm across, loosely attached at one end. Lobes strap-shaped, 1-3(-5) cm wide, more or less dichotomously divided, first adpressed, then mostly free from substrate in apical parts; apices truncate, sinuate-indented; upper surface grey-green to grey-brown, glossy, strongly reticulately ridged, with marked depressions. Cylindrical isidia or granular soredia sometimes present along margins and on ridges. Medulla white, often with internal cephalodia. Lower surface white to pale brown at margins and on the swellings corresponding to the depressions on upper surface, otherwise pale to dark brown, tomentose, except on the swellings, mostly erhizinate. Apothecia rare, laminal, especially on ridges, 2-5(-7) mm across, with a brown-red disc and a thin thalline margin. Asci 8-spored, Peltigera-type. Ascospores (1-)3(-5)-septate, fusiform to narrowly ellipsoid, 18-30 x 5-9 µm. Pycnidia immersed on the ridges. Conidia bacilliform, c. 5 x 1 µm. Photobiont chlorococcoid. Spot tests: cortex K-, C-, KC-, P-; medulla K+ yellow-orange (often faint), C-, KC+ yellow-orange, P+ faintly orange. Chemistry: stictic and constictic acids (major), norstictic, cryptostictic, and salazinic acids (minor).
Note: a mainly temperate, holarctic species found on bark and on epiphytic and epilithic mosses in humid forests; extinct in the plains of northern Italy, it is still abundant in humid montane forests of central and southern Italy, reaching the coast in undisturbed areas of Tyrrhenian Italy (e.g. in the Castelporziano Estate near Rome). A distribution map in Italy was published by Nascimbene & al. (2016). It is included in the Italian red list of epiphytic lichens under the “Least Concern” category (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)