Plants large, in dense tufts, yellowish, rufous proximally. Stems 1-3(-6) cm, erect, simple or 2-fid, tomentose proximally. Leaves erect, straight or somewhat homomallous when dry, erect-spreading when moist, lanceolate, 1.2-2 mm; margins strongly revolute, sharply serrulate throughout, teeth paired but often appearing in groups of 3 or 4 because of strongly revolute margins; apex acuminate; costa long-excurrent, distal abaxial surface scabrous; laminal cells , prorulose at distal ends, ; basal cells rectangular, 12-25 × 6-8 µm; medial and distal cells narrowly oblong, 18-35 × 3-5 µm. Specialized asexual reproduction absent. Sexual condition dioicous; perigonia gemmiform. Sporophytes unknown.
Philonotis sphaericarpa (Hedw.) Brid., Bryol. Univ. 2: 25. 1827.
Mnium sphaericarpon Hedw., Sp. Musc. Frond. 197. 1801. Bartramia sphaericarpa (Hedw.) P.-Beauv., Prodr. Aethéog. 44. 1805. Protologue: Jamaica. In Jamaica sin coll.
Philonotis sphaericarpa var. latirevoluta Card., Rev. Bryol. 38: 36. 1911. Protologue: Mexico. Etat de Puebla: Honey-station (Pringle, 1908, n°15317).
Plants small, medium, or large sized, in loose or dense, yellowish‑green or green, glaucous tufts, to 25 mm high. Stems red; rhizoids at base, reddish brown, smooth to lightly roughened. Leaves 1.2–2 mm long, erect, erect-spreading or spreading when dry, erect-spreading when wet, straight or secund, ovate-lanceolate; apices acuminate; margins narrowly revolute, singly or doubly serrate; costa short- to long-excurrent, excurrent part toothed; cells papillose, papillae at upper cell ends, upper cells rectangular, firm‑walled, 20–40 x 6–8 μm, basal cells rectangular, to 55 x 15 μm, alar cells quadrate. Dioicous. Perigonia gemmiform. Setae 15–25 mm long, red. Capsules 1.5–2 mm long, brown, subglobose, inclined to pendent; exothecial cells thick-walled; opercula 0.5 mm long, conic‑mammillate; peristome double, exostome teeth red, on outer surface densely and thickly papillose above, finely and evenly papillose below, 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 2–3, well-developed. Spores reniform, 22–30 μm, papillose.