Plants to 10 cm, in loose, irregular mats or dense pure cushions, yellow, yellow-green, or brown to blackish when growing suboptimally. Stems yellow, yellowish green, or yellowish brown; cross section pentagonal, cortical cells in 4-6 irregular layers, outer medulla cells thicker walled than inner, central strand conspicuous, sometimes degraded; rhizoids between leaves throughout plants, conspicuous when dry or moist, or visible among leaves at base of plants. Leaves distant and not covering rhizoids, or imbricate and rhizoids mostly hidden, undulate, twisted or straight when dry, erect-spreading when moist, broadly to narrowly lanceolate, widest at base, often concave; base not rounded to insertion; margins revolute usually one time, sometimes more, in proximal 2/3, irregularly serrulate at apex; apex acute, acuminate, or narrowed, rounded, and somewhat cucullate; costa flexuose; laminal cells rounded quadrate, short-rectangular, or elliptic, papillae large; basal cells often 2-stratose at insertion, walls brown. Specialized asexual reproduction by bullet- or spearpoint-shaped propagula, flat at attachment, in terminal cluster. Perigonia as terminal discoid splash platforms; paraphyses of 8-12 cells. Perichaetia with paraphyses absent. Seta 3-5 cm. Capsule inclined to horizontal, 3-4 mm; operculum short-rostrate, rostrum blunt; endostome cilia nodose. Spores 10-15 µm, smooth.
3. Aulacomnium palustre (Hedw.) Schwaegr. 皱蒴藓 zhou shuo xian Sp. Musc. Frond., Suppl. 3(1): 216. 1827. Sphaerocephalus palustris (Hedw.) Lindb., Musci Scand. 14. 1879. Gymnocybe palustris (Hedw.) Fries, Stirp. Agri Femsion. 27. 1825. Mnium palustre Hedw., Sp. Musc. Frond. 188. 1801. Type: Europe. Aulacomnium palustre var. papillosum (C. Müll.) Podp., Consp. Musc. Eur. 447. 1954. Aulacomnium palustre fo. papillosum Kab., Hedwigia 77: 128. 1937. Aulacomnium palustre subsp. papillosum (C. Müll.) Kindb., Eur. N. Amer. Bryin. 2: 337. 1897. Aulacomnium papillosum (C. Müll.) Jaeg., Ber. Thätigk. St. Gallischen Naturwiss. Ges. 1877–78: 451. 1880. Mnium papillosum C. Müll., Flora 59: 93. 1875. Aulacomnium palustre subsp. imbricatum (Bruch & Schimp.) Kindb., Eur. N. Amer. Bryin. 2: 338. 1897. Gymnocybe palustris var. imbricata (Bruch & Schimp.) Lindb., Not. Sällsk. Fauna Fl. Fenn. Forh. 9: 87. 1868. Aulacomnium palustre var. imbricatum Bruch & Schimp., Bryol. Eur. 4: 217. 1841. Plants rather robust, green or yellowish green, in dense tufts. Stems erect or slightly inclined, 10–15 cm high, branched, with dense rhizoids nearly throughout. Leaves densely imbricate, oblong-lanceolate to lanceolate, somewhat sheathing and slightly decurrent at base, acuminate at apex; margins plane, remotely or papillosely denticulate above, involute in the middle; costae slender, often flexuous above, ending below the apex; leaf cells rounded-hexagonal or irregularly rounded, clearly thickened at corners, unipapillose; basal cells at the insertion rectangular, often inflated, 2–3-stratose, thin-walled, smooth, sometimes brownish. Gemmae sometimes present on the stem apex. Dioicous. Setae elongate; capsules inclined, elongate-ovoid; neck short, yellow or yellowish brown; opercula shortly rostrate.