Beih. Nova Hedwigia, 79: 302, 1984. Basionym: Lecidea grossa Pers. ex Nyl. - Act. Soc. Linn. Bordeaux, 21: 385, 1856.
Synonyms: Catillaria grossa (Nyl.) Körb.; Catillaria leucoplaca auct. non (DC.) A. Massal.; Catillaria premnea auct. p.p.; Catinaria grossa (Nyl.) Vain.; Catinaria leucoplaca auct. non (DC.) Zahlbr.; Lecidea premnea Fr. non Ach.
Distribution: N - Ven, Lomb, Emil (Fariselli & al. 2020). C - Tosc, Marc, Umb (Ravera 2000, Ravera & al. 2006), Laz, Abr, Mol (Nimis & Tretiach 1999, Caporale & al. 2008), Sar (Zedda 2002, 2002b, Rizzi & al. 2011, Di Nuzzo & al. 2022). S - Camp (Aprile & al. 2003b, Nimis & Tretiach 2004), Pugl (Nimis & Tretiach 1999), Bas (Nimis & Tretiach 1999), Cal (Puntillo 1996), Si.
Description: Thallus crustose, episubstratic, smooth, rimose or warty, cream-coloured, greenish white or whitish grey, ecorticate, without a distinct prothallus. Apothecia lecideine, black, 0.4-1.5(-2.5) mm across, strongly constricted at base, with a concave to slightly convex, matt, epruinose, minutely roughened disc, and a thick, shiny, persistent or finally excluded proper margin. Proper exciple 80-160 μm thick laterally, layered, with a blue-green or emerald green inner and outer zone, K+ intensifying greenish, N+ purple-red, separated by a median, colourless zone inspersed with oil droplets, composed of radiating, coherent hyphae; epithecium blue-black, bluish green or diffuse olive, up to 10 μm high, K+ intensifiying green, N+ purple-red; hymenium colourless or partly pale reddish brown, (90-)120-140(-160) μm high, not inspersed with oil droplets, I+ pale blue; paraphyses lax in K, mostly simple, (1-)1.5(-2) μm thick at mid-level, the apical cells 3-4 μm wide; hypothecium not inspersed, reddish brown to greenish black, K+ reddish violet. Asci 8-spored, cylindrical-clavate, the K/I+ blue tholus penetrated by a faintly amyloid apical cushion with parallel or diverging flanks, the wall K/I-, surrounded by a K/I+ blue outer layer, Lecanora-type. Ascospores 1-septate, often slightly constricted at septum, hyaline, ellipsoid to oblong-ellipsoid, 20-34(-38) x 10-16 μm, the wall 1-2 μm thick. Pycnidia small, black, immersed. Conidia 3-4 x 1.5-2 μm. Photobiont chlorococcoid (according to some authors trentepohlioid, but with low amount of orange pigments), the cells 5-13 μm in diam. Spot tests: thallus K-, C-, KC-, P-, UV-. Chemistry: thallus without lichen substances.
Note: a mild-temperate to humid subtropical lichen found on base-rich bark of deciduous trees, especially of Acer and Fraxinus, locally still abundant in very humid forests of southern Italy but probably extinct in northern Italy. It is included in the Italian red list of epiphytic lichens as “Near-threatened” (Nascimbene & al. 2013c).
Growth form: Crustose
Reproductive strategy: mainly sexual
Most common in areas with a humid-warm climate (e.g. most of Tyrrenian Italy)