Plants light- to yellowish-green, glossy, in dense mats. Stems to 20 × 0.5--1 mm, prostrate to erect, irregularly branched with numerous short branches. Leaves imbricate, erect-spreading, smooth, usually concave, often symmetric, 0.7--1.5 × 0.2--0.5 mm, ovate-lanceolate, acuminate, margins plane or narrowly recurved nearly to apex, entire or sometimes with a few serrulations at apex; costa short and double, ending a short distance distal to leaf base, often lacking; leaf cells smooth, walls of basal cells pitted; median cells 52--150 × 4--10 μm; decurrent alar region triangular in outline, consisting of 1--5 vertical rows of rectangular cells, 26--72 × 12--19 μm, terminating in a single cell at the base. Specialized asexual reproduction by propagula usually present, 57--108 × 7--14 μm, consisting of 3--6 cells. Sexual condition dioicous, rarely fruiting. Seta light brown to orange-brown, straight, 0.6--1 cm. Capsule light brown to orange-brown when mature, erect, rarely inclined, straight or rarely somewhat arcuate, 0.5--1.2 × 0.2--0.6 mm, smooth, not contracted below mouth, slightly wrinkled at neck when dry; operculum conic-apiculate to short-rostrate, 0.4--0.6 mm; cilia lacking, or with 1--2 rudimentary cilia. Spores 9--13 μm.

Capsules mature summer. Swamps, fens, marshes, and inundated woods on rotten logs, stumps, bases of trees, and humus; 50--75 m; N.B., Nfld., N.S., Ont., Que.; Conn., Mass., Mich., N.J., N.Y., Pa., Wis.; Europe.

This is a rare species of northeastern North America where it always occurs in wet habitats. It is the smallest species in the genus and is recognized by short stems of up to 2 cm, erect-spreading, mostly symmetric, somewhat concave leaves that are 0.7--1.5 mm, median cells 4--10 μm wide, tapering decurrencies composed of rectangular cells, and erect, straight capsules that are not contracted under the mouth. Reports of this species from western North America are evidently erroneous and probably are mostly P. laetum, which it closely resembles.