Thallus of small lobes radiating up from the substrate, rounded, to 10 mm tall but usually less, to 2-3 mm broad; upper side smooth, dull or shining, brown, olive-brown, sometimes ashy-brown; lower surface whitish or pale brown, with scattered simple or slightly branched rhizinae. Upper cortex prosoplectenchymatous, to 25 μ thick; medulla loose, lower cortex like the upper. Apothecia very numerous, often obscuring the thallus; margin thick, smooth to crenulate, concolorous with the thallus; disk reddish brown, shining, epruinose, to 3 mm broad; epihymenium and upper part of the hymenium brown, paraphyses conglutínate; hymenium 50 μ, asci broadly clavate; spores 8, hyaline, simple, ellipsoid, 7-10 x 4.5-6.5 μ.

Reactions: K— , C— , KC— , P—.

Contents: protolichesterinic acid.

This species grows especially abundantly on the twigs of Betula, particularly the dwarf birches, but also occurs on the twigs and dead wood of other shrubs as Ledum, Rhododendron, Alnus, and Vacein-ium. It is a circumpolar species of the boreal forest and of the lower part of the arctic, growing in the tundras in low moist areas on the shrubs.