Plants small to medium-sized, dull. Stems prostrate or pendent; rhizoids from clusters of initials abaxial to leaf insertions, not or weakly branched; axillary hairs 240–360 µm. Leaves distant proximally, crowded distally, oblong-lanceolate to lanceolate, keeled, conduplicate; margins sometimes narrowly reflexed, entire or serrulate proximally, serrulate to serrate at apex; apex obtuse to acute; costa subpercurrent to percurrent; alar cells quadrate or rectangular, slightly enlarged, walls firm; medial laminal cells rhomboidal, linear-rhomboidal, or elongate. Perigonia lateral in leaf axils. Perichaetia with leaves elongate, sheathing setae. Seta 0.7–1.5 mm. Capsule immersed, oblong-cylindric to oval; annulus massive; operculum long-conic or occasionally obliquely rostrate; endostome trellis imperfect. Calyptra cucullate, covering only operculum. Spores 13–18 µm.
c, se United States.
Brachelyma is semi-aquatic; as with many semi-aquatic mosses, the plants can be slender to almost robust. Distinctive features include long, narrow, keeled-conduplicate, sometimes obscurely bordered leaves; strong, single costae; firm-walled, non-bulging alar cells; serrate to serrulate distal leaf margins; often rhomboidal distal laminal cells; long, sheathing perichaetial leaves, and short setae with completely immersed capsules. Curiously, the surface cells of the setae are quadrate to oblate; the result of simple cell elongation in these cells would give the Brachelyma setae the same length as the Dichelyma setae, as well as immersed or exserted capsules.