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.
Plants: to 12 cm, green to yellowish, brownish at base. Stems: with axillary hairs 180–220 µm, basal cell 1, quadrate, distal cells 3 or 4, long-cylindric. Leaves: weakly 3-ranked, strongly falcate to circinate at stem and branch apices, linear-lanceolate, 4–5 mm, medial stem leaves 0.4–0.8 mm wide; margins plane, entire; apex filiform-acuminate; costa long-excurrent; alar cells not or slightly enlarged; medial laminal cells 60–110 × 4–8 µm. Perichaetia: with leaves not or rarely overtopping capsule. Seta: 4–12(–20) mm. Capsule: emergent or short-exserted, oblong-cylindric to cylindric, 1–3 mm; operculum conic, 1–1.5 mm; exostome teeth spiculose-papillose; endostome yellowish brown to orange-red, spiculose-papillose, trellis perfect. Calyptra: 3–5 mm. Spores: 10–17 µm.
Tree trunks and branches (Acer, Alnus, Populus, Quercus, Salix, Toxicodendron), roots, shrubs, rock, swamps, bottom forests, flood plains, pond margins, frequently submerged. low to moderate elevations (0-1100 m). B.C., Ont., Alaska, Calif., Idaho, Mont., Oreg., Wash., Wyo.
Dichelyma uncinatum is corticolous (rarely on rock), and is distinguished by its strongly falcate to circinate leaves at stem and branch apices. Dichelyma capillaceum is similar to D. uncinatum in size, and both species have slender, linear-lanceolate leaves with setaceous apices and long-excurrent costae; in D. capillaceum the leaves at stem and branch apices are erect-spreading to flexuose-spreading and somewhat longer, the capsules are immersed or laterally emergent, and the endostomial trellises are incomplete. Dichelyma falcata has been confused with D. uncinatum because it sometimes has excurrent costae; however, D. falcatum is usually saxicolous and has much broader leaves (0.7–1.4 versus 0.4–0.8 mm wide) that are flexuose-spreading to falcate at the stem and branch apices. The remarkable record of D. uncinatum from southeastern Ontario (Parry Sound District, R. Ireland 22206 MO, NY) occurred mixed with a collection of D. falcatum.