Leaves ovate-lanceolate to short-subulate from an ovate or obovate base, serrulate at apex; costa excurrent or at least filling the leaf apex. Seta long, 10-30 mm. Capsule inclined, curved; neck as long as urn, long-cylindric, strumose at base; peristome teeth 2-fid or long-perforate, not fragile, commonly persistent; annulus compound, revoluble.
Trematodon ambiguus (Hedw.) Hornsch., Flora 2: 88. 1819. Dicranum ambiguum Hedw., Sp. Musc. Frond. 150. 1801. Syntypes. Sweden, Austria.
Plants scattered, yellowish green, terricolous; stems 3–10 mm long. Leaves evenly spaced, flexuous-spreading when wet, 2–3 mm long, oblong and clasping at base; apex abruptly contracted to a long awn; margins erect, entire; costa percurrent, smooth, ventral surface abruptly expanding at base of awn and filling the upper leaf; upper cells quadrate to shortly rectangular, thick-walled, basal cells narrowly long-rectangular to rhomboidal, whitish yellow, thin-walls. Autoicous. Setae 7–16 mm long, yellow; capsules inclined, yellow or red, urns ellipsoidal, 1.0–2.0 mm long, neck 1.2–1.5 mm long, as long as or a little shorter than the urn; annuli deciduous, revoluble; opercula rostrate, 1.0 mm long; stomata phaneropore; peristome teeth red, lanceolate, vertically striate. Calyptrae yellow, 1.5 mm long. Spores papillose.
1. Trematodon ambiguus (Hedw.) Hornsch. 北方长蒴藓 bei-fang chang-shuo xian Flora 2: 88. 1819. Dicranum ambiguum Hedw., Sp. Musc. Frond. 150. 1801. Syntypes. Sweden and Austria. 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.