Plants green with deep purplish undersides and margins; branching dichotomous, ventral intercalary branches occasional. Thalli 5 15 ´ 1 3 mm; epidermis smooth, cells thin walled, 25 35 ´ 25 28 µm, trigones small or absent, oil cells few, scattered; air pores surrounded by 2 3 tiers of 6 8 scarcely differentiated cells; ventral scales purplish with few oil cells; appendages 1 2, lanceolate. Sexual condition paroecious; androecia purplish groups of papillae posterior to bases of gynoecial stalks, occasionally on separate branches, then ovate; gynoecia terminal on dichotomous branches; stalks 1 3 cm, naked above, bases purplish with inconspicuous, subulate, deciduous scales; carpocephala hemispheric, 2 3 mm across, upper surface smooth, becoming low tuberculate on drying, 2 4 lobed below; pseudoperianths short, directed obliquely downward, the segments usually 8, free with age. Sporophyte capsules yellowish brown; spores yellow, 60 85 µm; elaters yellowish, 2 3 spiral, 150 200 µm.

Capsules mature Apr.--Aug. Moist soil over rock, usually calcareous in Arctic alpine areas; Greenland, Alta., B.C., N.W.T., Nun. (Baffin Island); Alaska, Ariz., Calif., Colo., Mich., Minn., Mont., N.Mex., Utah, Wyo; Europe; Asia.

This plant has been erroneously known in North America as A. Ludwigii (Schwaegrichen) Underwood and was listed as such in past publications. According to R. Grolle (1975) the type of A. ludwigii is Mannia triandra.