2. Dichelyma falcatum (Hedwig) Myrin, Kongl. Vetensk. Acad. Handl. 1832: 274. 1833.
Fontinalis falcata Hedwig, Sp. Musc. Frond., 299. 1801
Plants to 15 cm, green, yellowish, or yellow-brown. Stems with axillary hairs 200-300 µm, basal cells 1 or 2, quadrate, distal cells 4 or 5, long-cylindric. Leaves strongly 3-ranked, flexuose-spreading to weakly falcate at stem and branch apices, lanceolate, 3-5 mm, medial stem leaves 0.7-1.4 mm wide; margins plane or very narrowly recurved, entire proximally; apex acute, acuminate, or subulate; costa subpercurrent, percurrent, or variously excurrent; alar cells not or slightly enlarged; medial laminal cells 120-200 × 6-8 µm. Perichaetia with leaves not overtopping capsule. Seta 10-15 mm. Capsule exserted, oval to oblong-cylindric, 1-2 mm; operculum obliquely long-rostrate, 0.5-1 mm; exostome teeth finely papillose; endostome yellowish brown, finely papillose, trellis perfect. Calyptra 3-6 mm. Spores 12-14 µm.
Rock, tree bases, roots, in and along brooks, wet depressions, stream banks; low to high elevations (60-3400 m); Alta., B.C., Man., Nfld. and Labr., Ont., Que.; Alaska, Colo., Maine, Mich., Minn., N.H., N.Y., Utah, Vt., Wis., Wyo.; Europe; Asia (China).
Plants of Dichelyma falcatum are the largest in the genus. Critical features include strongly ranked, usually acute, lanceolate leaves that vary from erect to somewhat falcate at the stem and branch apices, exserted capsules, and perfect endostomial trellises; the leaves are about the same length as those of the other species but much broader. Dichelyma pallescens is often confused with D. falcatum, but the latter usually occurs on bark rather than rock and boulders. Both D. falcatum and D. uncinatum have long-excurrent leaves and exserted capsules with perfect endostomial trellises; D. uncinatum has more slender leaves that are strongly secund to circinate at the stem and branch apices.