Pterigynandrum filiforme Hedwig, Spec. Musc. 81. 1801.
Stem leaves imbricate, erect, somewhat falcate to homomallous, 0.6--1 mm, oblong-elliptic; margins narrowly reflexed below, erect and serrulate above; distal laminal cells oblong to rhombic, curved, abaxially prorulose. Seta 5--15 mm. Capsule 1--2.5 mm, symmetric; urn cylindric, erect; peristome diplolepidous, exostome teeth 16, short, lanceolate, endostome of 16 stout linear segments; calyptra cucullate. Spores 11--13 µm.
Mesic, acidic boulders and rock shelves in the western montane forests and on acidic rocks throughout the eastern Canadian shield country; Greenland; Alta., B.C., N.B., Nfld., N.W.T., N.S., Ont., P.E.I., Que., Yukon; Alaska, Calif., Colo., Idaho, Maine, Mass., Mich., Minn., Mont., N.H., N.Y., N.C., Oreg., Penn., S.D., Tenn., Vt., Va., Wash., W.Va., Wis., Wyo.; Europe; West Indies; Central America; Asia.
The slender, sleek, braided stems trailing down the sides of acid rocks are characteristic of the species. The somewhat curved, ovate, rather blunt leaves; and rhombic, coarsely prorulose leaf cells are identifying features.