1. Plagiothecium Bruch & Schimp. in B.S.G. 棉藓属 mian xian shu
Bryol. Eur. 5: 179. 1852. Hypnum sect. Plagiothecium (Bruch & Schimp.) Sull. in Gray, Manual (ed. 2) 679. 1856.
Plants slender to medium-sized, often complanate, green or yellowish green, usually glossy, in loose or dense mats. Stems prostrate or somewhat ascending, irregularly branched; in cross section a row of outer cortical cells enlarged, thin-walled; central strand absent or weakly to well differentiated; paraphyllia and pseudoparaphyllia absent. Stem and branch leaves similar, erect-spreading, plane, or sometimes undulate, often asymmetric, ovate to elliptical, or ovate-lanceolate, gradually or abruptly acute to acuminate, strongly decurrent at base; margins often recurved near base, sometimes throughout, entire or somewhat dentate at apex; costae double, or forked, unequal, appearing to be single, reaching 1/3–1/2 the leaf length, sometimes very short or absent; median leaf cells smooth, narrowly or elongate-rhomboidal, thin-walled; basal cells shorter, broader; alar regions often differentiated with loose, elongate-rectangular cells, thin-walled, hyaline, often strongly decurrent with long, narrow stripes in 2–3 rows. Brood bodies often present; gemmae single-celled, club-shaped, cylindrical, or fusiform, 2–7 celled, uniseriate, often clustered in leaf axils on stems and branches, sometimes borne on dorsal leaf surfaces, hyaline or light green. Autoicous or dioicous. Perichaetial leaves often sheathing at base, reflexed at apex. Setae slender, smooth, somewhat reddish when mature; capsules suberect, inclined or horizontal, symmetric or asymmetric, ellipsoidal or cylindrical, with a short neck; stomata present; opercula conic-rostrate with long, oblique beaks; annuli differentiated; peristome double; exostome teeth narrowly lanceolate, yellowish, cross-striolate below, hyaline, papillose above; endostome segments keeled, hyaline, papillose; basal membrane high; cilia 2–3, nodulose. Calyptrae cucullate, smooth. Spores spherical, nearly smooth or papillose.