Distribution: N - Frl (Grube & Giralt 1996), Ven (Sundin & Tehler 1998, Lazzarin 2000b), TAA (Nascimbene & al. 2007b), Lomb (Valcuvia & Truzzi 2007, 2007b), Piem. VA (Ongaro & al. 2022). C - Tosc. S - Camp (Ravera & al. 2018b), Pugl (Durini & Medagli 2004), Bas (Potenza 2006, Potenza & al. 2010, Potenza & Fascetti 2012, Ravera & al. 2021c), Cal (Puntillo 1996), Si (CLU 20822).
Description: Thallus crustose, endosubstratic, dull white, greyish brown to yellowish grey, smooth, thin, effuse, sometimes delimited by a dark prothallus, the thalline hyphae I-. Apothecia arthonioid, rounded to irregularly stellate in outline, 0.5-2 mm across, slightly immersed and level with thallus, with a black, epruinose, rough, often cracked disc, without a distinct margin, often disintegrating in the central part and peripherically regenerating as small segregated hymenial patches. Epithecium brown-black, 13-21 µm high, K+ greenish; hymenium colourless to pale brown, c. 35-50 µm high, I+ reddish, K/I+ blue; paraphysoids coherent, simple or sparingly branched in upper part, 1-1.5 µm thick; hypothecium dark reddish brown, 20-50 µm high. Asci 8-spored, broadly clavate, semi-fissitunicate, with a large apical dome, a distinct ocular chamber, and a K/I+ blue ring, Arthonia-type. Ascospores muriform, with 4-9 transverse septa and 1-3 longitudinal septa, hyaline to pale brown and faintly warted when old, obovoid to broadly ellipsoid, (15-)17-24(-26) x 7-9(-11) µm. Pycnidia hemispherical, brown to black, the wall red-brown, K+ greenish. Conidia bacilliform, 4-6.5 x 1-1.5 µm. Photobiont trentepohlioid. Spot tests: thallus K-, C-, KC-, P-. Chemistry: without lichen substances.
Note: a temperate-suboceanic lichen found on smooth bark of deciduous trees and shrubs (e.g. Alnus, Fagus, Fraxinus, Corylus, etc.) in humid deciduous forests, often on the basal parts of trunks; widespread, probably overlooked and more common in Italy than the few records would suggest.
Growth form: Crustose
Reproductive strategy: mainly sexual
Most common in areas with a humid-warm climate (e.g. most of Tyrrenian Italy)