Synonyms: Bacidia egenula (Nyl.) Arnold; Bacidia epiphylla Wheldon & Travis; Bacidia mediterranea B. de Lesd.; Bacidia peltigericola Vain.; Bacidia sbarbaronis B. de Lesd.
Distribution: N - TAA (Nascimbene & al. 2021), Lomb (UPS-L166833), Lig. C - Camp (Aprile & al. 2002), Cal (Puntillo 2011).
Description: Thallus crustose, episubstratic, finely granulose, continuous to rimose, glaucous green to greenish brown, consisting of (15-)20-60(-90) µm thick goniocysts. Apothecia biatorine, (0.15-)0.2-0.6(-0.8) mm across, with a grey-brown, bluish-brown to black, flat to slightly convex, epruinose disc, and a usually persistent, often paler, finally sometimes excluded proper margin. Proper exciple 30-50 µm wide laterally, without crystals, blue-green. green-brown to purplish brown in upper and outer parts, more or less colourless in lower and inner parts; epithecium blue-green, green-brown to green-black, K-, N+ violet-red, sometimes with brown spots reacting K+ purplish, N+ orange; hymenium colourless, 35-60 µm high (more than a third of the apothecium height); paraphyses rather coherent, mostly simple, 1-1.5(-2) µm thick at mid-level, the apical cells 2-6 µm wide; hypothecium orange-brown in upper part, colourless in lower part, the pigmented parts K+ green-brown. Asci 8-spored, clavate to cylindrical-clavate, the apical dome K/I+ dark blue with a pale, conical-pointed apical cushion (axial mass) never penetrating through the entire d-layer, the wall K/I-, but the thin outer gel K/I+ blue, Bacidia-type. Ascospores 3-7-septate, hyaline, acicular, clavate, or long-bacilliform, straight or slightly curved, (15-)25-40(-45) x 1.5-2.5 µm. Pycnidia semi-immersed in thallus, white. Conidia curved to sigmoid, 0-3-septate, 20-35 x c. 1 µm. Photobiont chlorococcoid. Spot tests: thallus K-, C-, KC-, P-, UV-. Chemistry: without lichen substances.
Note: a mild-temperate to humid subtropical species, most common on pebbles, old bricks or roofing tiles in shaded or semi-shaded habitats, also over moist ground in areas with siliceous substrata, sometimes on bark in the basal parts of trunks or on wood; certainly overlooked and probably more widespread in Tyrrhenian Italy, with outposts in the Insubrian District of the Alps.
Growth form: Crustose
Photobiont: green algae other than Trentepohlia
Most common in areas with a humid-warm climate (e.g. most of Tyrrenian Italy)