Thallus lemon-yellow, crustose, margin subeffigurate, crust abruptly limited, with high convex areolae, sometimes verruculose, continuous, lacking soredia, or the center rarely becoming farinose-sorediate.

Apothecia small, 0.3-1.5 mm, rare, black, sparse and dispersed or conglutinate, broadly attached; margin persistent, black, shiny; exciple exterior almost carbonaceous, dark reddish black, inner part bluish green; disk black, dull, rough; hypothecium pale, lower part brownish; epihymenium olive-green or bluish green; hymenium 100-150 µm; paraphyses slender, 1.7 µm, lax, not gelatinous; asci cylindrical or narrowly clavate; spores 8, hyaline, acicular, straight, tips acute, base slightly attenuate, 6-10-septate, 35-60 x 3-4 µm.

Reactions: thallus K—, C—, KC—, Lynge (1937) noted a P+ orange reaction which I have not been able to substantiate, but which may have been due to the Baeomyces over which the plant was growing. The exciple is K— or reddish, H2S04+ blue; epihymenium K+ reddish or olive, H2S04+ blue; hypothecium K+ reddish, HN03 or H2S04+ blue.

Contents: rhizocarpic acid (Huneck & Follmann 1972).

This species grows on soil and over humus, often beginning over Baeomyces thallus. It is circumpolar arctic-alpine, as it is known from Scandinavia, Greenland, Novaya Zemlya, Siberia, Jan Mayen Island, the Northwest Territories, and south to Colorado.

Arctic reports of Bacidia flavovirescens are generally this species, as already noted by Lynge (1937). That species, now known as Arthrorhaphis citrinella (Ach.) Poelt, differs in having larger spores, to 100 /xm long, and granular-sorediate. noneffigu-rate, flatter areolae of the thallus.