Mém. Soc. Sci. Nat. Math. Cherbourg 28: 131. 1892.
Plants green, yellowish, or brown. Stems to 30 cm; sclerodermis very thick, cortical cell walls firm; axillary hairs basal cells 1–3, subrectangular, reddish brown, distal cells 3–5, oblong, hyaline. Leaves erect to erect-spreading, imbricate, 2–4 mm; medial laminal cells 10–60 × 5–8 µm, marginal cells linear, 60–120 × 6–8 µm, forming weak border. Perigonia with leaves ecostate, antheridia few (4 or 5), paraphyses present. Perichaetia with leaves ovate-lanceolate to linear-lanceolate, 2–4 mm, margins entire, apex acute to long-acuminate, ecostate, archegonia many, paraphyses present. Seta with surface cells quadrate. Capsule 1.5–2.5 mm; annulus 8- or 9-seriate, persistent, cell walls thick; operculum 0.5–1.2 mm; exostome teeth inserted, orange or red, shorter than endostome, trabeculae widely spaced, papillose. Calyptra 2–3 mm.
Habitat: Tree trunks, branches, roots, bushes, logs, soil, rock, along rivers, flood plains and sloughs subject to inundation
Elevation: low to moderate elevations (0-300 m)
Ala., Ark., Fla., Ga., Ill., Ind., Ky., La., Md., Miss., Mo., N.C., Okla., S.C., Tenn., Tex., Va.
Brachelyma subulatum differs from Fontinalis by its costate leaves and cucullate calyptrae. Usually the presence of costae is enough to identify B. subulatum, but costal expression in Brachelyma is sometimes variable and appears environmentally induced. It is not unusual to find plants with keeled, strongly costate proximal leaves but concave, ecostate or weakly costate apical leaves. Brachelyma subulatum has been noted as lacking an annulus; in fact it has a massive, persistent annulus similar to those in many genera of Hookeriales. Dichelyma differs from B. subulatum in having longer setae and larger calyptrae that cover the capsule and often clasp the distal seta. Brachelyma subulatum appears to be a weak segregate of Dichelyma. Brachelyma subulatum differs from many other aquatic or semi-aquatic mosses in its keeled-conduplicate leaves.