17. Plagiothecium undulatum (Hedw.) Schimp. in B.S.G. 波叶棉藓 bo ye mian xian
Bryol. Eur. 5: 195. 1852. Buckiella undulata (Hedw.) Ireland, Novon 11: 55. 2001. Hypnum undulatum Hedw., Sp. Musc. Frond. 242. 1801. Type: Europe.
Plants rather large, stout, pale green, whitish green, or yellowish green, not or somewhat glossy, in thick mats. Stems prostrate, to 10 cm long, irregularly branched; leafy branches complanate, sometimes ascending, somewhat julaceous. All leaves imbricate, ovate to ovate-lanceolate, 2.0–5.0 mm × 1.0–2.3 mm, concave, slightly asymmetric, distinctly undulate, acute at apex; margins plane, entire or serrulate near leaf apex; leaf cells covered with minute, granular, cuticular papillae on abaxial surfaces; median cells narrowly rhomboidal, 96–175 µm × 7–11 µm, thin-walled; apical cells shorter; basal cells porose; alar regions decurrent, in a triangular shape, consisting of 1–3 rows of rectangular cells, ending with a single, elongate cell. Dioicous. Setae 25–45 mm long, brownish to reddish; capsules suberect to inclined, sometimes wrinkled, 1.5–4.0 mm long, often curved, constricted below the mouth when dry; opercula conic-rostrate, 0.8–1.2 mm long; annuli well developed, deciduous; cilia 2–3. Spores not seen.