Plants colonial from long-creeping rhizomes. Culms to 100 cm × (0.8-)1-1.2 mm distally. Leaves: blades flat, tip trigonous, channeled in cross section, to 40 cm × 1.5-6(-8) mm; distal leaf blade much longer than sheath. Inflorescences: blade-bearing involucral bracts 1-3, proximally blade, often sheath black, leaflike, longest 1-12 cm. Spikelets (1-)2-10, in subumbels, patent or pendent, ovoid, 10-20 mm in flower, 20-50 mm in fruit; peduncles 5-60 mm, smooth or scabrous; scales lanceolate or ovate, 5-10 mm, with prominent midrib fading proximal to tip, apex ± acute; proximal scales without lateral ribs. Flowers: perianth bristles 10 or more, white or pale yellow brown, 15-30 mm, smooth; anthers 2-5 mm. Achenes black, oblanceoloid, 2-5 mm. Eriophorum polystachion Linnaeus is a rejected name.
Extensively colonial from creeping rhizomes; stems subterete, 2-6(-9) dm; sheaths with a dark border at the top; blades ±flat for most of their length, 2-8 mm wide, the uppermost one mostly as long as or longer than its sheath; invol bracts unequal, 2 or 3 foliaceous, the longest one equaling or generally surpassing the infl; spikelets 3-several, on compressed, smooth or minutely scabrous-hirtellous pedicels to 5 cm; scales tawny to drab or blackish-green, lance-ovate, with a slender midvein not extending to the very thin, hyaline-scarious tip; bristles white; anthers 2-4.5 mm; achene blackish, rather narrowly obovate, 2-3 mm, 2-3 times as long as wide; 2n=58, 60. Bogs and marshes; circumboreal, s. to Me., N.Y., Mich., Io., Colo., N.M., and Oreg. Fr June-Aug. (E. polystachion, a rejected name)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.