Leaves ovate-lanceolate to long-subulate from an ovate or obovate base, serrulate at apex; costa percurrent or ending before the apex. Seta long, 10-30 mm. Capsule inclined, curved; neck 2-3 times as long as urn when dry, long-cylindric, strumose at base; peristome teeth 2-fid or irregularly perforate, not fragile, commonly persistent; annulus compound, revoluble.
Trematodon longicollis Michx., Fl. Bor. Amer. 2: 289. 1803. Type. U.S.A., North Carolina, in arenosis Carolinae, Michaux.
Plants scattered, yellow-green, terricolous, 3–5 mm long. Leaves evenly spaced, flexuous spreading when wet, clasping, oblong to oblong-ovate at base, gradually long linear-subulate above, 2–3 mm long; margins weakly recurved above, entire below, weakly denticulate by blunt teeth above; costa percurrent; upper cells short-rectangular, walls firm and thickened; basal cells laxly oblong-rhomboidal to long rectangular, pale whitish yellow. Autoicous. Setae 10–15 mm long, smooth, yellow; capsules inclined, yellow, urn ellipsoidal 1.5–2.0 mm long, neck 3.0–4.0 mm long; annuli deciduous, revoluble; opercula rostrate, 1.0 mm long; stomata crytoporic and phaneroporic stomata; peristome teeth red, lanceolate, vertically striate. Spores densely papillose or minutely warty.
2. Trematodon longicollis Michx. 长蒴藓 chang-shuo xian Fl. Bor. Amer. 2: 289. 1803. Type. U.S.A.: North Carolina, Michaux s.n. Trematodon acutus C. Müll., Syn. Musc. Frond. 1: 458. 1848. Trematodon drepanellus Besch., J. Bot. (Desvaux) 12: 283. 1898. Trematodon flaccidisetus Card., Beih. Bot. Centralbl. 17: 5. 1904. Trematodon drepanellus var. flaccidisetus (Card.) Dix., Hong Kong Naturalist. Suppl. 2: 2. 1933. Trematodon paucifolius C. Müll., Syn. Musc. Frond. 1: 459. 1848. Trematodon stristicalyx Dix., Hong Kong Naturalist. Suppl. 2: 3. 1933. Type. China: Zhejiang, Hang-zhou, E. D. Merril 1152 (holotype BM). Trematodon tonkinensis auct. non Besch. (sensu Chinese authors). Plants minute, 2–6 mm high, green to yellowish green, gregarious or scattered. Stems erect, simple or rarely branched. Leaves 1.7–3.6 mm long, contorted when dry, flexuose spreading when moist, oblong to oblong-ovate at base, gradually narrowed from a clasping base to a long, linear-subulate acumen, blunt at tips; margins plane and entire below, slightly recurved and serrulate above; costa strong, percurrent, not entirely filling the acumen; upper and median cells short to moderately rectangular, 18–24 µm × 8–10 µm, firm or somewhat thick-walled; basal cells in the clasping base, oblong-rhomboidal to long-rectangular, 40–90 µm × 8–13 µm, lax, thin-walled. Autoicous. Perichaetial leaves larger than the upper stem leaves. Setae straight, (4–)10–20(–30) mm long, yellow to yellowish brown; capsules inclined, urn short-cylindric, 1.5–2.0 mm long, neck 3.0–5.0 mm long, curved above, strumose at base; opercula slenderly and obliquely long-rostrate; annuli well developed, deciduous; stomata of two kinds; peristome teeth lanceolate, reddish, somewhat perforate, vertically striate on lower 2/3 of the teeth, papillose on the upper 1/3. Spores ca. 20 µm in diameter, strongly papillose.
The wider definition of this species is adopted here. A capsule neck that is consistently twice as long as the urn, strongly perforated peristome teeth without free filaments, and papillose spores without obvious tetrad scar, separate T. longicollis from the other species. Although gametophytically similar to several other species, identification has not been a problem, as all collections examined have numerous sporophytes.
Plants small to medium, gregarious or in loose tufts, green; terricolous. Stems 1-7 mm high; in section central strand large, cortical cells large, lax, becoming smaller with thicker walls toward margin. Leaves contorted above erect base dry, erect to spreading wet; oval to oblong, abruptly subulate, 2-4 mm long; apex bluntly acute; base sheathing; margin bistratose in subula, with a few projecting cells above, apex frequently toothed. Costa subpercurrent to percurrent; in section flattened, guide cells 6, ventral stereid band small, 3-4 cells in single central row, ventral surface cells smaller than guide cells, covering entire costal surface or restricted to area above ventral stereid band and exposing guide cells laterally, dorsal stereid band 1-3 cells thick, extending across costa, dorsal surface cells smaller than guide cells, occasionally some cells larger, extending upward interrupting stereid band. Laminal cells short-rectangular to quadrate above shoulders; basal cells large, lax, rectangular to oblong-hexagonal. Perichaetial leaves oblong-subulate, 3-4 mm long. Seta 6-15 mm long, yellowish; capsule erect, yellow, urn cylindical, 1.2-1.6 mm long, neck 2.2-3.5 mm long, strumose; peristome reddish, teeth lanceolate, 340-360 µm high, perforated, without free filaments, vertically barred below, upper segments papillose, yellowish, fringe present between teeth, weak, papillose, hyaline; operculum long-beaked, 1.0-1.5 mm high; calyptra cucullate; spores round, 22-25 µm, bluntly papillose.
Plants small to medium-sized, gregarious or in loose tufts. Stems 1-7 mm long. Leaves contorted above erect base when dry, oval to oblong, abruptly subulate, 2-4 mm long; apex bluntly acute; base sheathing; margins bistratose in subula; costa subpercurrent. Laminal cells short-rectangular to quadrate; basal cells large, lax. Capsule erect, urn cylindrical, neck twice as long, strumose; peristome reddish, teeth lanceolate, fringe present between teeth. Spores papillose.