Philonotis fontana (Hedw.) Brid., Bryol. Univ. 2: 18. 1827.
Mnium fontanum Hedw., Sp. Musc. Frond. 195. 1801. Bartramia fontana (Hedw.) Turn., Muscol. Hibern. Spic. 107. 1804. Protologue: Locis paludosis apertis spongiosis. Maio et Junio sporangia maturat. Perenne.
Plants medium to large-sized, in dense yellowish green or green, glossy tufts, to 80 mm high. Stems red, densely tomentose below; rhizoids reddish brown, smooth. Leaves 1.4–2.1 mm long, moderately spaced, erect to erect-spreading when dry, erect-spreading when wet, straight or secund, ovate-lanceolate; apices slenderly long-acuminate; margins narrowly revolute, jugate, singly or doubly serrate; costa long-excurrent; cells papillose, papillae at lower cell ends on median and basal cells, papillae at upper cell ends on apical cells, upper cells sublinear, rectangular or oblong, firm‑walled, 12–38 x 5–7 μm, basal cells rectangular to subquadrate, 12–30 x 5–8 μm, alar cells quadrate in 2–3 rows. Microphyllous branches sometimes present in leaf axils. Dioicous. Perigonia discoid. Setae straight, 2–4 cm long. Capsules inclined, 2–4 mm long, ovoid to subglobose, furrowed when dry, striate when wet; exothecial cells short, thick-walled; opercula conic, 0.3–0.5 mm long; peristome double, exostome teeth narrowly triangular, to 500 μm, outer surface finely papillose below, coarsely papillose near tips, trabeculae thin, inner surface smooth, trabeculae thick, endostome nearly as long as the exostome, yellowish, finely papillose granulose below, segments split along the median line and each half diverging toward the cilia, cilia 3–4, well-developed. Spores ovoid or subreniform, 20–30 μm, coarsely papillose. [Sporophytes and gametangia unknown in Central America, description based on North American material.]