Sphagnum arcticum sp. nov.

Sphagnum arcticum (Sect. Acutifolia) is known by the brown color and habit of the plants, the pale brown or yellowish-brown stem sclerodermis, the occurrence of scattered pores in the surface cells of the stem hyalodermis, and the lingulate to sometimes lingulate-spathulate stem leaves, which are obtuse to obtuse-truncate and fimbriate-lacerate at the apex. The new species shows closest affinity to S. subfulvum Sjors, S. fimbriatum Wils. and S. girgensohnii Russ. It is reported from Svalbard, Greenland, Siberia and Arctic Canada. While revising the collections of Sphagnum from Svalbard (Flatberg & Frisvoll, in prep.), we found an undescribed species belonging to Sect. Acutifolia. Herbarium studies also yielded specimens from Greenland, Siberia and Arctic Canada. SPHAGNUM ARCTICUM Flatb. et Frisv., sp. nov. FIG. 1-22 Sphagnum Sect. Acutifoliorum. Plantae ? robustae, plerumque ferrugineo-fuscae; cylindrus caulis lignosus luteo-fuscus vel subfuscus; epidermis caulina parietum exteriorum cellularum superficalium saepe foramine uno instructa; folia caulina lingulata vel lingulato-spathulata, apice late rotundato vel truncato, media tantum parte laciniatofimbriato. Type: Norway. Svalbard: Spitsbergen, Todalen, 78*10'N, 15050'E, 20 July 1976, Brattbakk s.n. (TRH-holotype; C, H-isotypes). Fig. 19-22. Plants moderately robust in dense cushions, usually brown or golden brown, or less commonly variegated green and yellowish-brown, without metallic luster when dry. Capitulum brown, flat to slightly convex, and with straight to erect-incurved, patent branches which taper towards an acute tip. Terminal bud visible but not conspicuous. Stem hyalodermis 2-4 layered, the surface cells (Fig. 6) aporose or (more rarely) porose with 1 (rarely 2) semicircular to elliptical pore usually closely facing the cell end, or rarely circular and free-lying. Stem sclerodermis small-celled, thick-walled and pale brown to yellowish-brown. Branch fascicles densely crowded, each fascicle of 2 divergent and 1 pendent branches; divergent branches stout, terete, patent to erecto-patent and usually somewhat incurved; pendent branch usually longer, thinner and paler. Leaves of divergent branches (Fig. 9-13, 20) unranked, densely imbricate and straight to slightly subsecund, broadly lanceolate to ovate-lanceolate and subcucullate at the apex; length (1.1)1.4-1.8(2.1) mm; breadth to length ratio (0.40)0.45-0.51(0.55); hyalocysts at the mid-median convex surface of the leaf (Fig. 16-17) with (5)8-10(12) semicircular to elliptical, ringed and commissural pores, at the base on the same surface with (3)5-8(12) larger, elliptical or semicircular often irregular pores in each hyalocyst; hyalocysts at the concave surface of the leaf (Fig. 14-15) aporose or sometimes with 1(-2) distal end pores at the upper median half of the leaf, at the leaf margin pores more numerous; chlorocysts (Fig. 18) in transverse section equilateral-triangular to trapezoidal-triangular, broadly exposed on the concave surface of the leaf, slightly enclosed or just reaching the convex surface; resorption furrow absent. Stem leaves (Fig. 1-5, 19, 21-22) patent, erecto-patent or erect-appressed to the stem, narrowly to broadly lingulate or sometimes lingulatespathulate and with a broadly obtuse to obtusetruncate and more or less fimbriate-lacerately resorbed apex; length (1.1)1.2-1.4(1.6) mm; breadth to length ratio (0.45)0.55-0.64(0.70); border in upper half narrow (2-5 cells wide) and often indistinct, in lower half widened and filling up 1/3 to 1/2 (more rarely 2/3) of the leaf breadth at the base; hyalocysts at e upper end of the leaf (Fig. 7) broadly S-shaped to rhombic-S-shaped, predominantly unseptated or septated into 2(-4) parts, usually aporose and efibrose; lateral margin at the upper end sometimes with 1 or 2 rows of distinctly enlarged and subquadrate hyalocysts (Fig. 8, 21). Inflorescence and s orophyte unknown. Ecology. According to Eurola (1971: Tab. 1, as S. subfulvum), S. arcticum grows at the edge of 007-2745/84/143-148$0.75/0 This content downloaded from 207.46.13.21 on Tue, 27 Sep 2016 04:07:44 UTC All use subject to http://about.jstor.org/terms 144 THE BRYOLOGIST [Volume 87