Thallus to 20 cm broad, usually less, monophyllus, stiff, with folds or pleats centrally, the edges tom or deeply cut; upper surface smooth, dull, olive-brown; underside olive-brown, darker toward the umbilicus, with papillate lamellae and trabeculae which form platelike layers over the underside; lower cortex areolate. Thallus 210-280 µ thick, cortex thin, brown, medulla about 33 µ, lower cortex thick 130-180 µ. Apothecia common, adnate, in indentations in the upper side, convex, of free gyri, branching dichotomously, lacking a common exciple around the edge; parathecium black externally, brown internally; hypothecium indefinite, hymenium 85-99 µ, paraphyses unbranched, septate, 3.5 µ; asci with 8 spores, spores simple, hyaline, 8.5-13 x 3.5-5 µ.

Reactions: K—, C+ red, KC+ red, P—.

Contents: gyrophoric acid.

This species grows on acid rocks, including sandstones. It has a disjunct Asian-eastern North America range. In the latter it occurs from the Great Bear Lake region east to Newfoundland, south to South Carolina. Llano (1950) reported a specimen “between Point Barrow and Mackenzie River, Capt. Pullen, 8/1849.” It has not subsequently been collected this far to the northwest of the rest of its range. Neither has this species been found on Greenland.