Plants cespitose; rhizomes brownish, short, tough, fibrous. Culms: fertile ones upright or reclining; nodes sometimes with axillary bulblets. Leaves 5-9 per culm; sheaths of proximal leaves green to whitish or brown; proximal sheaths and blades with septa many, conspicuous; blades 32-68 cm × 7-13(-16) mm. Inflorescences terminal, rarely also with 1 lateral inflorescence from distal leaf axil; rays all arching or sometimes 1 or 2 ascending, distal branches scabrous, proximal branches smooth, rarely scabrellous, rays sometimes with axillary bulblets; bases of involucral bracts green, margins usually speckled with red-brown, not glutinous. Spikelets in clusters of 2-18 (largest cluster with 8 or more), spikelets sessile, ovoid to narrowly ovoid, 3-5 × 2-3 mm; scales brown or blackish brown with greenish midribs, elliptic, 1.5-2.5 mm, apex slightly mucronate, mucro 0.05-0.1(-0.2) mm. Flowers: perianth bristles persistent, 6, stout, straight or curved, slightly shorter to slightly longer than achene, with retrorse, thick-walled, sharp-pointed teeth densely arranged in distal 0.6-0.9, enclosed within scales; styles 3-fid. Achenes pale brown, elliptic to obovate in outline, plano-convex, 1.1-1.7 × 0.6-0.8 mm. 2n = 54. Fruiting late spring-early summer (Jul). Growing in wet depressions, bogs, sinkhole ponds, or adjacent to pools; 100-1100 m; Que.; Md., Mass., N.H., N.Y., Pa., Vt., Va., W.Va. Scirpus ancistrochaetus occasionally hybridizes with S. hattorianus. Scirpus ancistrochaetus once grew in Washington County, New York; it is apparently no longer present in the state. Scirpus ancistrochaetus is in the Center for Plant Conservation´s National Collection of Endangered Plants.