Bryologist 5: 76. 1902. -- Brachythecium latifolium Kindb., Forh. Vid. Selsk. Christiana 1888(6): 8. 1888
Plants in soft, loose mats, grass-green to emerald-green, irregularly and sparingly branched with the branches prostrate to ascending. Primary stems to 15 cm long with leaves not much different from those on the branches. Leaves to 2.5 mm, about 2: 1, symmetric and straight but with the acumen laterally twisted, lightly or not at all concave and smooth to lightly wrinkled, never plicate, broadly ovate, loosely imbricate to approximate. Leaf apices acuminate but with the acumen not well-demarcated. Margins entire to serrulate at immediate base, becoming serrate by leaf middle and dentate or nearly so near the apex, somewhat recurved at base but plane above, very narrowly decurrent by a 1–2 cell wide strip which extends nearly to insertion of next lower leaf. Median cells smooth, spinulose and thin-walled, to 8 µm wide, mostly 8–15: 1, not pitted. Basal juxtacostal cells similar to adjacent alar cells. Alar group poorly demarcated and only gradually differentiated from more distant cells of leaf, extending from margin to costa. Alar cells to 30 µm wide, 1–3: 1, thin-walled and pellucid. Marginal cells of alar region narrowly rectangular, to 18 µm wide, to 6: 1. Costa extending 1/2 to 3/4, tapering to apex, obscurely spinose distally. Juvenile leaves to 100 µm long, broadly ovate, about 1.5: 1, entire across the acuminate apex. Axillary hairs persistent, to 100 µm, 3–4 celled with a single basal brown cell, thin-walled throughout with some diameter increase in the distal cells. Rhizoids sparse, mostly unbranched, light-brown to reddish-brown, smooth, to 12 µm in diameter, clustered on the abaxial leaf base. Stem cross-section with central strand, a stereome 2–3 cells thick, but without an hyaloderm.
Dioicous with male plants typically somewhat smaller than the females. Perigonia sparingly produced on prostrate stem and large branches. Perichaetial leaves to 2.5 mm long, ecostate, sheathing at base but reflexed on the abruptly contracted acumen. Seta coarsely papillose distally but sometimes almost smooth near the base, to 25 mm long, distally geniculate. Capsule dark brown to reddish brown, inclined to horizontal, strongly arcuate, not distorted or sulcate when dry. Urn to 2.5 mm, 2–3: 1. Exothecial cells irregular in size and shape, 15–20 µm wide, 1–3: 1, thick-walled with lumen: wall ratio about 3: 1. Stomata present on slightly raised pustules at base of capsule, short and vertical pored. Operculum conic, about 1/4 as long as urn. Annulus present, of two rows of thick-walled cells. Exostome teeth to 450 µm long, narrowly lanceolate and obscurely shouldered, about 8: 1, tapering to a very narrow tip, horizontally striate, yellow to pale yellow. Endostome segments lightly papillose, very narrow, about half as long as exostome, with basal membrane about as long as the segments. Cilia 1–3, smooth and articulate. Spores smooth, 12–15 µm.