Closed-sheath cotton-grass, linaigrette à anthères courtes

Eriophorum opacum (Bjørnstrom) Fernald; E. vaginatum Linnaeus var. opacum Bjørnstrom

Plants cespitose. Culms terete or nearly so, 20–70 cm, smooth. Leaves: bladeless sheaths 1–3, evenly distributed on culm, distal to middle, not inflated distally, filiform, channeled, 0.4–1.2 mm wide. Inflorescences: involucral bracts absent. Spikelets solitary, erect, globose, 10–20 mm in flower, 20–35 mm in fruit; proximal empty scales usually 7 or more, ascending, blackish, ovate-lanceolate, 5–10 mm, thin, margins broad, ribless, midrib not reaching tip. Flowers: perianth bristles usually more than 8, creamy white to pale brown, 10–20 mm; anthers 0.5–2 mm. Achenes oblanceoloid, (1.8–)2–2.3(–2.7) × 0.5–1.2 mm; apex minutely apiculate, 0.1 mm. 2n = 58.

Fruiting summer. Bogs, fens, tundra, muskeg, wet soils; 0–1500 m; Alta., B.C., Man., Nfld. and Labr., N.W.T., Nunavut, Ont., Que., Sask., Yukon; Alaska; Eurasia.

Eriophorum brachyantherum var. pellucidum Lepage is ca. 30 cm with narrowly oblong achenes (2.5–2.7 mm). It is known from only a single station (Rupert House, Quebec) and may be a hybrid between E. brachyantherum and E. vaginatum subsp. spissum. Further study is needed to determine the status of this plant.