Sphagnum platyphyllum Warnstorf 1884

Sporophytes are uncommon in Sphagnum platyphyllum, which can be quite variable in size and the development of branch fascicles, with some forms even being simplex while other forms may have up to three branches per fascicle. The species can usually be recognized by the large stem leaves that are spreading and easily visible because of the scarcity of hanging branches. It should also be noted that in this species and S. contortum the 2-3-layered stem cortex is not an entirely consistent trait, as plants quite typical in all other respects are occasionally found with the cortex only 1-layered, at least in part.

Plants small to moderate-sized, unbranched or sparsely branched; green, golden brown to brown, capitulum small with a large and conspicuous terminal bud. Stems green to brown; superficial cortex of 2-3 layers of enlarged, thin-walled cells. Stem leaves broadly ovate, 1.2-2.2 mm; straight; apex rounded; hyaline cells non-septate, convex surface with numerous small pores (less than or equal to ¹/6 cell diameter) forming a continuous row along the commissures, concave surface aporose or with a few scattered pores along the commissures and cell ends. Branches short and blunt, sometimes lacking completely and plants simplex. Branch fascicles of 1-3 branches, 1-2 of these spreading, branches usually not numerous. Branch leaves broadly ovate, 1.4-2.5(-3) mm; straight; apex rounded; hyaline cells as in stem leaf. Sexual condition dioicous. Capsule exserted, with few pseudostomata. Spores 23-35 µm; papillose on both surfaces, with indistinct Y-mark sculpture on distal surface; proximal laesura 0.5 spore radius or less.

Plants rather stout and robust, grayish green, tinged with brownish color, in loose tufts. Stem cortex in 1–3 layers, hyaline cells large, thin-walled, without fibrils, mostly porose; central cylinder yellowish brown. Stem leaves 1.0–1.8 mm × 0.8–1.0 mm, broadly ligulate to elliptic, concave, margins involute, borders differentiated; hyaline cells rarely divided, fibrillose, or sometimes indistinct, with a few small, ringed pores at the ends and corners on both surfaces. Branches in fascicles of 3–5, with 2–3 spreading. Branch leaves 1.5–2.2 mm × 0.8–1.2 mm, broadly ovate to elliptic, strongly concave, margins involute, borders narrowly differentiated, obtuse and denticulate at the apex; hyaline cells with a few, small pores at the corners on the ventral surface, with more ringed pores, often scattered at margins along commissural rows on the dorsal surface; green cells in cross section elliptic, centrally located, exposed equally on both surfaces. Dioicous. Sporophytes not seen.

Distribution: China, Japan, Russian Far East and Siberia, Europe, Greenland, and North America.

Habitat: in bogs and wetlands near streams.

Sphagnum laricinum var. platyphyllum Lindberg, Not. Sällsk. Faun. Fl. Fenn. Förh. 13: 403. 1874; S. contortum var. platyphyllum (Lindberg) Åberg, S. grasslii H. A. Crum; S. subsecundum var. platyphyllum (Braithwaite) Cardot

Sphagnum subsecundum var. platyphyllum (Braithw.) Card., Bull. Soc. Bot. Belg. 25(1): 73. 1886. Sphagnum subsecundum ssp. playtphyllum (Braithw.) Herib., Mém. Acad. Sci. Clermont-Ferrand, sér. 2, 14: 454. 1899. Sphagnum contortum var. platyphyllum (Braithw.) Åberg, Ark. Bot. 29A(1): 34. 1937. Sphagnum isophyllum Russ., Arch. Naturk. Liv-Ehst-Kurlands, Ser. 2, Biol. Naturk., 10: 415. 1894.