Sphagnum acutifolium Schrad. var. robustum Russ., Arch. Naturk., Liv-Ehst-Kurlands, Ser. 2, Biol. Naturk. 7: 117. 1865, hom. illeg. Sphagnum acutiforme Schlieph. & Warnst. var. robustum Warnst., Flora 67: 501. 1884. Sphagnum robustum (Warnst.) Röll, Flora 69: 109. 1886.

Plants variable in size and color, stout or slender, soft, pale green or yellow, tinged with reddish color, in dense cushions. Stem cortex in 2–4 layers, hyaline cells without fibrils, with a large pore in each cell; central cylinder pale yellowish or reddish. Stem leaves 0.8–1.3 mm × 0.6–0.9 mm, variable in size, usually broadly ligulate, rounded, denticulate or somewhat lacerate at the apex; borders narrow above, suddenly widened near the base; hyaline cells rhomboidal, usually undivided, without fibrils and pores, or rarely with the traces of fibrils and small pores in the upper cells. Branches in fascicles of 4–5, with 2–3 spreading. Branch leaves 0.8–1.6 mm × 0.5–0.9 mm, ovate-lanceolate, gradually to abruptly acuminate, reflexed near the apex when dry, blunt and denticulate at the apex; margins involute, cucullate above, borders differentiated; hyaline cells with pores at the corners in the upper cells and numerous pores here and there on the ventral surface, with elliptic pores at the opposite ends along commissural rows on the dorsal surface; green cells in cross section isosceles-triangular or trapezoidal, exposed more broadly on the ventral surface, enclosed by hyaline cells on the dorsal surface or slightly exposed on both surfaces. Dioicous or monoicous; antheridial branches purple red. Perigonial leaves similar to vegetative branch leaves. Perichaetial leaves broadly ovate, blunt at the apex, borders indistinct, with hyaline and green cells in the upper half, with almost only green cells in the lower half, hyaline cells without fibrils. Spores yellowish, smooth, 21–32 µm in diameter.

Type. Europe.

Chinese specimens examined: HEILONGJIANG: Xiao Xing An Ling (Lesser Khingan Mt.), S.-E. Liu 8849 (KUN). NEI MONGOL: Da Xing An Ling (Greater Khingan Mt.), C. Gao 1019, 1024 (IFSBH, KUN). SICHUAN: Emei Shan (Mt.), P.-C. Chen 51, 5545 (KUN), T. N. Liou 10253 (KUN), D.-D. Tao 7601 (KUN), Z.-W. Yao 1125, 2828 (KUN); E-bian Co., S.-E. Liu 12623 (KUN); Hong-xi Co., Z.-T. Guan 9003 (KUN); Tian-quan Co., Q. Li 2731 (KUN, MO), Z.-L. Wu 11760 (KUN), J.-L. Yang 2007 (KUN), M. Zang 4670 (KUN); Xi-kang Co., X.-C. Duan 1088, 1176 (KUN). XIZANG: Cha-yu Co., M. Zang 5136 (KUN, MO), D.-C. Zhang 5146, (KUN, MO), A.-L. Zhang 33(d) (KUN), D.-C. Zhang 646, 653 (KUN), 827 (KUN, MO); Li-jiang Co., G.-M. Feng 9446 (KUN); Wei-xi Co., Q.-W. Wang 31403, 31476 (KUN, PE); near Myanmar border, Handel-Mazzetti 9946 (H, KUN).

Habitat: usually on wet humic soil under coniferous forests; also in bogs and on ground near streams; Distribution: China, Japan, Russian Far East and Siberia, Europe, Greenland, and North America.

This species is quite common in southwestern and northeastern China. It often occurs in large, dense cushions producing sporophytes. The branch leaves of this species are similar to those of Sphagnum squarrosum with reflexed leaf apices, but it differs from the latter in having smaller, slender, and softer plants with tightly imbricate branch leaves.

Illustrations: C. Gao (ed.) 1994 (Pl. 18, figs. 4–13, as Sphagnum robustum).