Thallus variable, ranging in size from single, pusilloid erect lobes to large thalli almost a meter across; the lobes imbricate, up to 4 cm. across and several cm. long, the margins ascending, some forms crisped or proliferate; upper surface dark greenish blue when moist, slaty or bluish or greenish gray or brownish when dry, smooth, shining; under surface with broad, flat, white, or usually, brown or black, reticulated veins with very small white interspaces, rhizoids sparse, short and fasciculate or in one variety over 5 mm. long and simple. Algal layer continuous, 20-30 µ thick; upper part of the cortex plectenchymatous 30 µ thick, hyaline to pale brown, medulla of very loosely interwoven hyphae 8 in diameter with a lumen of 5 µ; medulla 200-700 µ thick. Hymenium 100-110 µ thick; hypothecium about 60 ix thick. Algae 3-6 µ in diameter. Apothecia medium sized, 2-5 mm. in diameter, on erect narrow lobules at the ascendent tips of the lobes, sometimes borne in pairs, the sides usually reflexed, the disk reddish or chestnut brown to black, the margin crenate, the reverse corticate; hypothecium brown; hymenium hyaline; asci cylindrico-clavate, 80-105 x 10 µ, 8 spored; the spores acicular, slightly curved, 48-105 x 3-4 µ (Tuckerman reports 69-90 x 3-4; Fink reports 60-100 x 3-4).

Reactions: K—, C—, KC—, P—, I stains the asci blue, no other part being affected.

Contents: tenuiorin, dolichorrhizin, zeo-rin, unidentified substances.

This species grows on soil, moss, logs, rocks, and bases of trees in moist woods and is reported to be cosmopolitan. It ranges throughout North America but appears to be lacking in the Arctic Islands other than Baffin Island.