Stereodon curvifolius (Hedwig) Mitten

Plants medium-sized to large, light green to yellow-green, . Stems 4-10 cm, orange-brown to reddish, procumbent to suberect, sparsely branched, regularly pinnate, branches1.5 cm; hyalodermis absent, central strand weakly differentiated; pseudoparaphyllia foliose. Stem leaves falcate-secund, ovate, narrowing to apex, 1.5-2.5 × 0.7-0.8 mm; base slightly decurrent, auriculate, sometimes only on one side; margins plane, sinuate to entire basally, gradually weakly toothed near apex; acumen relatively broad; costa double, short; alar cells , region well defined, , in 1-3 rows across base; basal laminal cells broader than medial cells, pigmented, walls not porose; medial cells 70-80 × 4-5 µm. Sexual condition dioicous; . Seta orange-yellow to brownish when mature, 2-4.5 cm. Capsule inclined to horizontal, reddish, obovoid-cylindric, 2.5-3 mm; annulus broad, 2-seriate; operculum conic; endostome cilia 2 or 3.

Capsules mature Jul-Aug. Terrestrial, decaying logs in woodlands, rock, peatlands; low to high elevations (0-2000 m); N.B., Nfld. and Labr. (Nfld.), N.S., Ont., P.E.I., Que.; Ala., Ark., Conn., Del., D.C., Ga., Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Nebr., N.H., N.J., N.Y., N.C., Ohio, Okla., Pa., R.I., S.C., Tenn., Tex., Vt., Va., W. Va., Wis.

Hypnum curvifolium might be confused with H. lindbergii; it differs in its more plumose branching, more circinate leaves, and lack of stem hyalodermis. Also, H. lindbergii has a more extensive and often decurrent alar region. Hypnum imponens is distinguishable by its usually smaller habit size and toothed pseudoparaphyllia. Hypnum curvifolium has stems 0.5-3 mm wide; the leaves are curved to the insertion with enlarged, hyaline alar cells; the supra-alar cells are ovoid to triangular and smaller than the alar cells; the laminal cells are sometimes projecting abaxially at the distal ends; the capsules are plicate when dry; and the endostome cilia are nodulose. Sporophytes are produced in summer.