Thallus crustose, olive-green to whitish green, partly slightly pruinose, continuous to areolate to strongly verrucose-warty, lacking soredia or isidia; hypothallus indistinct. Apothecia immersed in areolae, appearing like Pertusaria; disk black, concave deeply, at first ostiolate, becoming broader, with a thin darkening border around ostiole within thalloid margin; hypothecium pale yellowish or brownish; epithecium K—, HC1—, HN03—; hymenium hyaline, inspersed at times, 1+ blue; paraphysoids slender, 1.5 µm, branched but not anastomosing, lax, tips only slightly thickened, not much darkened; asci clavate; spores 8, biseriate, thin-walled, wall single, ellipsoid, often containing oil drops, walls K—, 30-65 X 16-36 µm.

Reactions: K—, C—, KC—, P—.

Contents: unknown.

This species grows on moss, humus, and soil in the Arctic but also on tree trunks toward the southern edge of the range. It is circumpolar arctic-alpine; and boreal, and also occurs in the Andes in South America. In North America it ranges south to North Carolina, Minnesota, New Mexico, and California.

Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2007. Lichen Flora of the Greater Sonoran Desert Region. Vol 3.

Thallus: rather well delimited, verrucose, surface: ±uneven, whitish gray or brownish gray Apothecia: as in M. [verrucosa var.] verrucosa (generic description) cospores: 34-60 x 30-42 µm. Substrate and ecology: on bark of the trunk and branches of broad-leaved, non-resinous trees (often on Quercus; but also on Juniperus deppeana, Pinus edulis, and Pseudotsuga menziesii), mostly on the bases of ancient trunks; most frequent in the lower montane belt, 700-2860 m World distribution: Europe, Macaronesia; Saudia Arabia, and North America Sonoran distribution: Arizona, southern California, Baja California, and Chihuahua. Notes: Megaspora verrucosa var. mutabilis has different substrates and different altitudinal preferences than M. verrucosa var. verrucosa in western North America. The former's thallus is rather well delimited, being rimose and its surface is whitish to yellowish or brownish gray. Its hymenium is shorter, and its ascospores are somewhat longer and narrower. The thallus of M. verrucosa var. mutabilis also tends to be bare to weakly pruinose and non-scabrous (with granules or crystals mainly in the medulla rather than the epinecral layer), but this is somewhat variable in both varieties.