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.