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 × 4–5 µm. 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, longer than exostome teeth, 0.3 mm beyond mouth, papillose distally, not perforate, never split, cilia simple. Spores: 11–14 µm. Phenology: 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 PotosÃ, 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.