Distribution: N - Ven, TAA (Nascimbene & al. 2007b), Emil (Watson 2014, Fariselli & al. 2020). C - Tosc (Loppi & Frati 2006), Abr. S - Camp.
Description: Thallus crustose, mostly endosubstratic, continuous to finely rimose, very thin to evanescent, whitish to pale fawn, ecorticate, usually forming large patches, without a distinct prothallus, the hyphae I+ and K/I+ pale blue. Apothecia rare, arthonioid, adnate, 0.4-1 mm across, 90-210 µm tall, with a slightly to strongly convex, densely white-pruinose disc, without a distinct proper margin. Proper exciple not well-developed; epithecium grey to brown, inspersed with pale crystals- 10-25 µm high; hymenium colourless to pale yellowish brown, 45-65 µm high, I and K/I+ blue; paraphysoids 1-1.5 µm thick at base, apical cells up to 2 µm wide; hypothecium dark brown. 50-120 µm high. Asci 8-spored, clavate, semifissitunicate, without K/I+ blue tholus structures, Arthonia-type. Ascospores (2-)3-4(-5)-septate, hyaline, narrowly obovate, (11-)13-19(-23) x (4-)5-7(-8) µm, with a slightly larger apical cell. Pycnidia emergent, 0.15-1.4 mm in diam., dark brown to black but thickly white-pruinose at least at the base, flattened to urceolate, with pale brown conidial masses usually protruding from the apical pore, the wall K+ greenish black, N+ slowly orange-brown. Conidia bacilliform, straight, (4-)5-6 x 1-1.5 µm. Photobiont trentepohlioid. Spot tests: thallus K-, C-, KC-, P-. Chemisty: byssaceum-unknowns, probably 2'-O-methylperlatolic acid and one accessory compound.
Note: a mild-temperate species found on very old deciduous trees with acid bark (in Italy oaks) in open woodlands, often near rivers. Most Italian records are old, and the species was included as “Regionally Extinct” in the Italian red list of epiphytic lichens (Nascimbene & al. 2013c).