Bot. Mag. Tokyo, 35: 70, 1921. Basionym: Urceolaria actinostoma var. caesioplumbea Nyl. - Bull. Soc. Linn. Normandie, sér. 2, 6: 264, 1872.
Synonyms: Diploschistes actinostoma var. caesioplumbeus (Nyl.) J. Steiner
Distribution: N - Lig. C - Tosc, Sar (Neuwirth 2018). S - Si (CLU 10396).
Description: Thallus crustose, episubstratic, well-delimited and forming large patches, cracked-areolate, consisting of irregularly angular, 0.4-1.5 mm wide, flat to slightly convex, blue-grey to dark lead-grey, glossy, smooth, epruinose areoles. Apothecia common, perithecioid, immersed in the thallus, usually 1 per areole, up to 1.6 mm across (in section), with a blackish, urceolate to finally flat disc not visible from above, being concealed by a thick, radially sulcate, often pruinose proper margin. Proper exciple up to 70 µm thick, carbonized, pseudoparenchymatous; epithecium poorly differentiated, colourless to brownish; hymenium colourless, 130-170 µm high, non-amyloid; paraphyses flexuose, 1-1,5 µm thick, not swollen at apex; hypothecium colourless, 10-15 µm high. Asci 4-8-spored, cylindrical to subclavate, the wall evenly thickened, with an abrupt apical thickening and a thin internal apical beak, lacking an apical apparatus, the contents I+ orange-red, the walls I-, not fissitunicate. Ascospores muriform, with 4-7 transverse and 1-4 longitudinal septa, at first hyaline then pale brown, ellipsoid, 28-45 x 12-25 µm. Photobiont chlorococcoid. Spot tests: thallus K-, C+ red, KC-, P-, UV-. Chemistry: lecanoric acid.
Note: a mild-temperate lichen found on base-rich, mostly coastal siliceous rocks in the supralittoral zone, widely distributed along the Atlantic and Mediterranean coasts and exclusively Tyrrhenian in Italy; it often the starts the life-cycle on Lecanora gangaleoides. Earlier records from Emilia and Trentino (see Nimis 1993: 278), being dubious, are not accepted here.
Growth form: Crustose
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly sexual
Most common in areas with a humid-warm climate (e.g. most of Tyrrenian Italy)