Plants green above, purplish along margins and underneath, the thalli curl upward around apical margins exposing white scale appendages, forming a conspicuous apical tuft; branching dichotomous, ventral intercalary branches infrequent. Thalli 5 10 ´ 2 3 mm; epidermis smooth, cells 20 ´ 30 µm with slightly thickened walls and small trigones; air pores indistinct, surrounded by 1 3 tiers of 5 7 scarcely differentiated cells, oil cells few, scattered; ventral scales deep purple, long tapered, with scattered oil cells; appendages 1 2, white, long tapered lanceolate to acuminate, as long or longer than scales, curling up around the anterior thalli margins, forming conspicuous white clusters at apices. Sexual condition paroecious, occasionally autoecious; androecia form ill defined dorsal streaks of papillae at posterior bases of gynoecial stalks or on nearby branches; gynoecia terminal on main thalli, stalks 1 2 cm, purplish with cluster of white hairlike scales at bases and none at apices; carpocephala 2 3 mm across, ovate, at least 1 1/2 times taller than wide with 3 4 lobes directed downward; pseudoperianths conical, of 6 8 white segments, connate at apices. Sporophyte capsules yellowish; spores yellow to pale brown, 80 90 µm; elaters yellowish, 1 3 spiral, 150 200 µm.

Capsules mature May. Soil in rock crevices, usually calcareous in arctic alpine areas; Greenland; Alta.; Alaska, Minn., Mont., Wash.; Europe; Asia.

The white scale appendages exposed at thalli apices and along upturned margins are distinctive. These scale clusters have caused confusion with Mannia fragans, which has a similar apical cluster. Unconfirmed reports from areas south of this species' range may represent M. fragans, which also lacks a pseudoperianth and has brown, not yellow spores.