Description. [Modified from Tehler 1990] Thallus crustose, endophloeodal or incoherently epiphloeodal, effuse, smooth or slightly rugose often with leprose parts (due to soralia), epruinose, white to whitish grey, 0.10-0.15 mm when measurable; prothallus not seen. Vegetative diaspores soredia in soralia; soralia occurring near and around the ascomata, maculate or thallus in parts nearly dissolved into soredia; maculae 0.15-0.6 mm in diameter; soredia 0.01-0.03 mm diam. PhotobiontTrentepohlia, cells coccal (with a characteristic fluorescence), 15-35 pm, homoiomerous, a cyanobacteria is sometimes also present on the thallus surface making the thallus appear dark grey. Ascomata numerous, evenly dispersed over thallus surface, multiascal locules, pluricarpocentral (hymenial strands present), discothecia, solitary, developing mutually with the thallus, circular in outline or slightly elongated, sessile or sometimes nearly immersed, base not or only rarely constricted, 0.15-0.8 mm diam. Disk exposed, convex, black, smooth to finely verrucose, when young with a thin white pruina that usually disappears with age. Thalline margin when young conspicuous but poorly developed, without algae and cortex, when old disappearing or dislocated; proper exciple a thin parathecium, sometimes inconspicuous. Hypothecium distinct, dark brown (carbonaceous), extending down to substrate. Hymenium 60-70 μm; paraphysoids parallel, separable, sparsely branched, hyaline, 1-2 pm in diameter, septate with cells ~ 7-9 μm long. Epithecium brown, 15-20 pm; gel brown, granular; hyphae loosely intertwined, sparsely branched, more or less easily separable, with tips clavate, 2-4 μm diam., conspicuously verrucose, brown; calcium oxalate absent. Asci clavate, often poorly developed, 60 x 10 μm; ascospores narrowly fusiform, usually with one end tapering more than the other, slightly sigmoid to curved, smooth, 3-septate, not constricted at flat septa, hyaline, 32-37 x 3-4 μm. Conidiomata pycnidia, solitary, immersed or slightly elevated, black or brown, 0.05-0.15 mm diam.; conidia cylindrical bacilliform, curved, hyaline, 4-6 x 1-2 μm.
Chemistry.Spot tests: thallus C-, K-, PD (not investigated), I-, K/I-; hypothecium K - (oliveblack), I-, K/I-; hymenium, K-, I+ blue sometimes negative, K/I+ conspicuously blue; epithecium, K-, I+ blue sometimes negative, K/I+ conspicuously blue; asci I-, KI+ blue tip with pore; pycnidial wall K- (olive-black), I- , KI+ blue basal part of pycnohymenium. Secondary product: roccellic acid.
Substrate and habitat. Corticolous on old bark of hardwoods and conifers, less often lignicolous on wood.
Distribution. Europe and North America; in North Carolina found in the Blue Ridge ecoregion.
Literature
Acharius, E. (1799) Lichenographiae Svecicae Prodromus 264 pp. (original description as Lichen pericleus).
Branth, J.S. & E. Rostrup (1869). Lichenes Daniae, eller Danmarks lavar. Botanisk Tidsskrift. 3: 127-284.
Tehler, A. (1990) A new approach to the phylogeny of Euascomycetes with a cladistic outline of Arthoniales focussing on Roccellaceae. Canadian Journal of Botany68: 2458-2492.