1. Trematodon ambiguus (Hedw.) Hornsch., Flora. 2: 88. 1819; Dicranum ambiguum Hedw., Sp. Musc. Frond. 150. 1801.
Plants very small, 5–7 mm high, yellowish green, gregarious or scattered. Stems erect, usually simple. Leaves 2–3 mm long, erect or somewhat contorted when dry, erect-spreading when moist, oblong, clasping at base, abruptly narrowed from the shoulder to a long-awned, blunt apex; margins plane, entire; costa strong, filling the entire acumen, smooth on the back; leaf cells at the shoulder irregularly short-rectangular to rhombic, 13–26 µm × 5–8 µm, rather thick-walled; basal cells narrowly long-rectangular, 40–90 µm × 8–13 µm, rather thin-walled, lax, with several narrower cells (4–5 µm wide) near the margins. Autoicous. Perichaetial leaves similar to the upper stem leaves. Setae straight, 16–20 mm long, yellowish; capsules inclined, urns short-cylindric, 1.2–2.0 mm long, neck 1.3–2.0 mm long, strumose at base; opercula long-rostrate; annuli well developed, deciduous, revoluble; stomata superficial; peristome teeth reddish, linear-lanceolate, vertically striate nearly to the tips, finely papillose at the tips. Spores 26–30 µm in diameter, yellowish, strongly papillose.
Syntypes. Sweden and Austria.
Chinese specimens examined: HEILONGJIANG: Dailing Pref., P.-C. Chen & C. Gao 676 (IFSBH). SICHUAN: Ping-wu Co., Q. Li 10275 (IFSBH). YUNNAN: Kunming City, Z.-R. Zhang 74 (KUN); Meng-la Co., Redfearn et al. 33758, 34122 (MO).
Habitat: on wet soil and disturbed places by streams; Distribution: China, Nepal, India, Myanmar, Japan, Russian Far East, Europe, North and Central America.
Illustrations: T. Cao & C. Gao 1988 (Fig. 6).