Plants typically small and slender; capitulum small and with a conspicuous terminal bud; green to yellowish brown. Stem leaves broad-spatulate, 0.8-1.5(-2) mm, strongly lacerate across the broad apex and partway down the sides, border scarcely to moderately broadened at leaf base (0.25 width of base or less. Sexual condition monoicous. Spores 20-27 µm, finely papillose on both surfaces; proximal laesura less than 0.5 spore radius.
Capsules mature late spring and early summer. Minerotrophic, common at the mineral soil margins of bogs and poor fens, medium open and forested fens; low to high elevations; Alta., B.C., Man., N.B., Nfld. and Labr. (Nfld.), N.S., Ont., Que., Sask.; Alaska, Calif., Colo., Conn., Del., Idaho, Ill., Ind., Iowa, Ky., Maine, Md., Mass., Mich., Minn., Mo., Mont., N.H., N.J., N.Y., Ohio, Oreg., Pa., R.I., Tenn., Vt., Wash., W.Va., Wis.; South America; Eurasia; Pacific Islands (New Zealand).
Sporophytes are very common in subsp. fimbriatum. It is associated with Sphagnum centrale, S. fallax, S. henryense, S. affine, S. palustre, S. russowii, S. teres, S. warnstorfii, and Drepanocladus exannulatus. It is normally very easily recognizable because of its very small size, pale green color, and distinct terminal bud. In Alaska it overlaps with subsp. concinnum, which has a similarly very broad and lacerate stem leaf apex but the lacerate margin does not extend down the sides of the leaf. Subspecies concinnum is also a more compact-growing taxon with a distinctly browner color.
Plants: typically small and slender, larger and compact in the Arctic, capitulum small to moderate-sized, often with a conspicuous terminal bud; green, yellowish brown to brown; without metallic lustre when dry. Stems: pale green to straw-colored; superficial cortical with a large round pore in distal portion of cell free from cell wall. Stem: leaves spatulate to broad-spatulate, 0.8–1.5(–2) mm, strongly lacerate across the broad apex and often part way down the margins, border scarcely to strongly broadened at base (0.25 width of base or less); hyaline cells rhomboid, efibrillose and often 1–2-septate. Branches: not 5-ranked, quite terete, long, and slender Branch fascicles with 1– 2 spreading and 1–2 pendent branches. Branch: leaves ovate to ovate-lanceolate; 1.1–1.5(–2) mm, slightly concave, straight; apex involute; margins entire; hyaline cells on convex surface with numerous pores along the commissures grading from small pores near leaf apex to large pores at base, concave surface with large round pores at leaf apex and along margins. Sexual: condition often monoicous. Spores: 20–27 µm, finely papillose on both surfaces; proximal laesura less than 0.5 spore radius. North America, South America, Eurasia, Pacific Islands (New Zealand).