Leskea polyantha Hedwig, Sp. Musc. Frond., 229. 1801; Isothecium polyanthum (Hedwig) Spruce; Pterogonium polyanthos (Hedwig) Muhlenberg; Pylaisia cyrtophylla Kindberg; P. denticulata Schimper ex Sullivant; P. filari-acuminata Müller Hal. & Kindberg; P. jamesii Sullivant & Lesquereux; P. ontariensis Müller Hal. & Kindberg; P. polyantha var. jamesii (Sullivant & Lesquereux) Rau & Hervey; P. polyantha var. subdenticulata (Schimper) Rau & Hervey; P. pseudoplatygyrium Kindberg; P. subdenticulata Schimper; P. suttonii Jennings; Pylaisiella polyantha (Hedwig) Grout; P. subdenticulata (Schimper) Grout; Stereodon polyanthos (Hedwig) Mitten; S. subdenticulatus (Schimper) Mitten

Plants yellowish or whitish. Stems terete-foliate to flattened, somewhat regularly pinnate, branches 10 mm, creeping or rarely ascending and curved, subjulaceous; pseudoparaphyllia triangular, long-acuminate. Stem and branch leaves slightly differentiated. Stem leaves nearly straight, ovate-lanceolate, gradually narrowed to apex, concave, slightly plicate, 1.3-2 × 0.4-0.5 mm; margins plane, sometimes slightly involute distally; acumen long; costa double, short; alar cells 8-10 along margins, in 5-8 rows; medial laminal cells 50-80 × 4-5µm. Branch leaves narrowly ovate-lanceolate, shorter, 1.1-1.4 × 0.3-0.5 mm. Seta 1-1.8 cm. Capsule erect, oblong-cylindric, 1.6-2.2 × 0.4-0.6 mm; exothecial cells rounded-rectangular; operculum conic, obliquely short- pointed; peristome perfect, long; exostome teeth lance-subulate, 0.2 mm, base 70 µm wide, slightly papillose distally; endostome free, basal membrane well developed, segments linear-subulate, , papillose distally, not perforate, never split, cilia simple. Spores 11-14 µm.

Capsules mature fall-winter. Tree trunks; low to high elevations; Alta., B.C., Man., N.B., Nfld. and Labr., N.W.T., N.S., Nunavut, Ont., P.E.I., Que., Sask., Yukon; Ala., Alaska, Ariz., Colo., Conn., D.C., Ill., Iowa, Ky., Maine, Mass., Mich., Minn., Miss., Mo., Mont., Nebr., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Pa., R.I., S.Dak., Tex., Vt., Va., Wis.; Mexico (Nuevo León, San Luis Potosí, Veracruz); Europe; Asia (Russia).

Pylaisia polyantha is the type species of the genus; it is the most widely distributed of the species and is remarkably variable. More than 20 varietal taxa have been described, but they are yet to be revised (T. Arikawa 2004). The capsules are somewhat widened at the base.