Obtuse Bog Moss

Sporophytes are uncommon in Sphagnum obtusum. This is a quite phenotypically variable species that warrants further investigation, which may result in taxonomic splitting. The strongly obtuse stem leaf should separate it from any similar species with which it occurs. Sphagnum mendocinum looks similar phenotypically but there appears to be no range overlap with S. obtusum. The tiny branch leaf pores, which may seem like no more than pinpricks in the cell surface, easily separate S. obtusum microscopically from other species of sect. Cuspidata.

Plants rather large, 8–12 cm high, pale green, tinged with yellowish brown, in loose or compact tufts. Stem cortex in 2–4 layers, hyaline cells large, thin-walled, without fibrils and pores; central cylinder pale yellowish brown, not clearly differentiated from cortical cells. Stem leaves 1.0–1.5 mm long, distantly set, triangular-ligulate, rounded, dentate or sometimes lacerate at the apex; borders narrow above, clearly widened below (ca. 1/3 the leaf base width); hyaline cells broadly rhomboidal, occasionally divided and fibrillose in the upper apex. Branches in fascicles of 4–5, with 2–3 spreading. Branch leaves 2.0–3.0 mm long, ovate-ligulate to lanceolate, undulate when dry, slightly involute near apex; hyaline cells linear-rhomboidal, densely fibrillose, with numerous, small, pore-like membrane thinnings in 1–2 rows on both surfaces; green cells in cross section narrowly isosceles-triangular, exposed on the dorsal surface, enclosed by hyaline cells or sometimes slightly exposed on the ventral surface. Dioicous. Sporophytes not seen.

Plants moderate to robust, weak-stemmed, yellow, yellowish brown to golden brown; capitulum varying from rounded, not 5-radiate and twisted to flat 5-radiate and straight branched. Stem pale green to pale brown; superficial cortex of weakly to moderately differentiated. Stem leaves triangular-lingulate, 0.9-1.3 mm; usually appressed; apex obtuse and often erose; hyaline cells efibrillose and nonseptate. Branches tapering or in more robust forms, frequently blunt, straight to arcuate, leaves slightly to moderately elongated at distal end. Branch fascicles with 2 spreading and 2 pendent branches. Branch stems green, with cortex enlarged with conspicuous retort cells. Branch leaves ovate to ovate-lanceolate; more than 1.8 mm; straight, stiff, not much undulate and reflexed to recurved; margins entire; hyaline cells on convex surface with a few end pores, but mostly numerous small to very small (often barely visible) pores or wall thinnings free from the commissures, on concave surface similar, but with pores generally fewer and larger; chlorophyllous cells triangular in transverse section, just reaching concave surface or slightly enclosed. Sexual condition dioicous. Spores 18-27 µm; both surfaces covered with rough, irregular verrucate plates of papillae, bifurcated Y-mark sculpture on distal surface; proximal laesura less than 0.5 spore radius.

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

Habitat: in open bogs.

Sphagnum recurvum var. obtusum (Warnst.) Warnst., Hedwigia 23: 121. 1884.

Sphagnum obtusum Warnst. Bot. Zeit. 35 : 478. 1877
Plants robust, green or tinged yellowish or brownish. Wood-cylinder yellowish-green; cortical cells of the stem hardly differentiated, the outer cells of the stem long-quadrilateral, without fibrils or pores: stem-leaves medium-sized, triangular-lingulate, somewhat eroded at the broad apex but not cleft, the border of 3-6 rows of narrow cells above, slightly wider below; hyaline cells narrow, not divided, mostly without fibrils, their membrane on the inner surface largely resorbed, on the outer surface the resorption confined to a few apical cells: branches in fascicles of 4 or 5, 2 spreading, their cortical cells in a single layer, the retort-cells with an inconspicuous neck: branch-leaves somewhat undulate when dry with spreading tips, lanceolate, involute in the apical part, the apex toothed, the border entire, of 2-5 rows of very narrow cells; hyaline cells fibrillose, narrowly linear-rhomboidal, in the basal portion 8-10 times as long as wide, shorter above to 6 times, on the inner surface with pores only in the ends of the cells, on the outer surface with similar pores, also in the lower side-regions with small round membrane-thinnings visible only when the leaf is stained, these varying in number, in an irregular single or double row in each cell: chlorophyl-cells triangular in section with the base exposed on the outer surface, the apex of the triangle just reaching the inner surface of the leaf, its legs frequently more or less curving and its apex well included; hyaline cells not convex on the outer surface, considerably so on the inner, up to one fourth of the diameter of the cell.
Dioicous. Antheridia in catkins on spreading branches; antheridial leaves brown, smaller than the normal branch-leaves.
Type locality: Germany.
Distribution: Greenland; reported from Ontario; also in Europe and reported from Asia.