23. Dicranum polysetum Swartz, Monthly Rev. 34: 538. 1801.
Dicranum undulatum Ehrh. ex Web. & Mohr, Index Mus. Pl. Crypt. 2. 1803, hom. illeg.
Plants medium-sized to large, 2–10(–15) cm high, green to yellowish green or golden brown, shiny, in dense tufts. Stems erect or ascending, often branched, densely tomentose nearly throughout. Leaves not much altered or somewhat flexuose when dry, erect-spreading or sometimes irregularly falcate-secund when moist, lanceolate, up to 10 mm long, gradually narrowed from an oblong base to a slender, keeled, usually undulate acumen, apex narrowly acute; margins plane, or slightly recurved on one side below the middle, serrate in the upper half; costa narrow, subpercurrent to percurrent, ridged or lamellate in 2 serruate rows at back above the middle; upper cells short-rectangular, ca. 50 µm × 9 µm, thick-walled, somewhat porose, sometimes mammillose at back; basal cells elongate, linear-rectangular, thick-walled, somewhat porose; alar cells quadrate or hexagonal, inflated, bistratose, thin-walled. Dioicous. Male plants dwarfed, located at lower part of the females. Setae straight, often aggregate, 2–5 per perichaetium, 2.5–4.0 cm long, yellowish, becoming reddish with age, twisted when dry; capsules cylindric, 3–4 mm long, strongly curved, inclined to horizontal, asymmetric, furrowed when dry and empty, not strumose; opercula long-rostrate, 2.5–4.0 mm long; annuli none; stomata present; peristome teeth lanceolate, ca. 0.6 mm long, unequally divided to the middle, brownish or reddish brown, papillose above, vertically striolate below. Spores 19–26 µm in diameter, minutely papillose.
Chinese specimens examined: HEILONGJIANG: Da Xing An Ling (Greater Khingan Mt.), C. Gao 13189 (IFSBH); Mu-ling Co., C. Gao 13653 (IFSBH, MO); Ning-an Co., C. Gao 6705 (ALTA, IFSBH). JILIN: An-tu Co., C. Gao 1206, 16352 (IFSBH), C. Gao 26860 (MO); Chang-bai Co., C. Gao 7336, 7497 (IFSBH, MO), C. Gao 22205 (MO); Wu-song Co., S.-E. Liu 8881 (MO). NEI MONGOL: Da Xing An Ling (Greater Khingan Mt.), P.-C. Chen & C. Gao 938, 996 (IFSBH), C. Gao 6785, 12740 (IFSBH, MO), K.-X. Zhuo 2142 (ALTA, IFSBH); Man-gui, C. Gao 12710 (ALTA, IFSBH). XIZANG: Mi-lin Co., Y.-G. Su 5223 (IFSBH, KUN). YUNNAN: Gong-shan Co., M.-Z. Wang 9436 (b)(IFSBH, PE).
Habitat: on humic soil in bogs, rocks, or rotten wood; Distribution: China, Korea, Japan, Russia, Europe, North Ameica.
This species is easily recognized by its strongly undulate leaves and aggregated setae.
Illustrations: C. Gao (ed.) 1994 (Pl. 127, figs. 1–8).