Description: Thallus crustose, very variable, from endosubstratic to rimose-areolate or even bullate-areolate, dirty white to ivory white. Cortex 15-30 μm thick, colourless or pale brown; medulla white, I-. Apothecia lecideine, black, sessile and strongly constricted at base, 0.2-0,6(-1) mm across, with an initially flat, then convex, sometimes botryose, epruinose disc, and a very thin, soon excluded proper margin. Proper exciple 25-45 μm wide, dark to pale green in outer part, colourless within; epithecium blue-green to rarely olive-green, N+ reddish, 2-10 μm high; hymenium colourless or pale green, 35-60 μm high, I+ blue; paraphyses mostly simple, strongly coherent, 1.7-2 μm thick at mid-level, the apical cells to 5 μm wide; hypothecium colourless, pale blue-green or pale violet, 20-200 μm high. Asci 8-spored, clavate, with a K/I+ blue apical dome penetrated by a narrow, K/I- apical cushion surrounded by a narrow, deeply K/I+ blue zone, the wall K/I- but surrounded by an I+ red-brown, K/I+ blue outer layer, the ocular chamber relatively small, Biatora-type. Ascospores 1-celled to rarely 1-septate, hyaline, ellipsoid to narrowly ellipsoid, (6.5-)8-11(-18) x (2.5-)3-5(-6) μm. Pycnidia dark brown to black. Conidia bacilliform, 4-9 x 0.6-1.4 μm. Photobiont chlorococcoid. Spot tests: thallus K-, C-, KC-, UV-. Chemistry: without lichen substances.
Note: an arctic-alpine, probably circumpolar species of basic to weakly calciferous siliceous rocks in exposed situations, with optimum above treeline. For further details see Hertel & Rambold (1995). Earlier records of Lecidea conferenda from Liguria, Toscana and Sardegna (see Nimis 1993: 380), being dubious, are not accepted here.