Scirpus polyphyllus Vahl

Scirpus polyphyllus occasionally hybridizes with S. atrovirens.

Plants cespitose; rhizomes short, tough, fibrous. Culms: fertile ones erect or reclining; nodes sometimes with axillary bulblets. Leaves 14–22(–26) per culm; sheaths of proximal leaves green or brownish; proximal sheaths and blades with septa usually few, inconspicuous; blades 16–31 cm × 5–8 mm. Inflorescences terminal, rarely also with 1 lateral inflorescence from distal leaf axil; rays divaricate, smooth throughout or scabrous distally, rays usually with axillary bulblets; bases of involucral bracts green, not glutinous. Spikelets in dense clusters of 3–9 (largest cluster with 6 or more), spikelets sessile, broadly ovoid, 2.5–4 × 1.6–3 mm; scales reddish brown with green midribs, circular or nearly so, 1–1.5 mm, apex mucronate or occasionally short-awned, mucro or awn 0.2–0.3 mm. Flowers: perianth bristles persistent, 6, stout, contorted, much longer than achene and projecting beyond it, retrorsely barbed in distal 1/2, exserted from scales at maturity; styles 3-fid. Achenes pale brown, obovate or nearly obtriangular in outline, plumply trigonous or plano-convex, 1.1–1.4(–1.8) × 0.8–1 mm. 2n = 58.

Ala., Ark., Conn., D.C., Ga., Ill., Ind., Ky., Md., Mass., Miss., Mo., N.H., N.J., N.Y., N.C., Ohio, Pa., S.C., Tenn., Vt., Va., W.Va.

Fruiting summer (Jul–Aug).

Along wooded streams and other swampy places, usually shaded by trees; 0–1000m.

Scirpus polyphyllus Vahl, Enum. 2: 274. 1805
Scirpus exallatus Pursh, Fl. Am. Sept. 56. 1814.
Scirpus exallatus @ viviparus Pursh, Fl. Am. Sept. 56. 1814.
Scirpus brunneus Muhl. Descr. Gram. 42. 1817.
Scirpus brunneus /3 viviparus Torr. Ann. Lye. N. Y. 3: 327. 1836.
Scirpus brunneus y crispus Torr. Ann. Lye. N. Y. 3: 327. 1836.
Holoschoenus brunneus Steud. Nom. Bot. ed. 2, 1: 773. 1840.
Perennial; roots spongy, the rootstocks short; culms single at the nodes, usually ca. 6 dm. tall, to 1 m., triangular, green, smooth; sheaths green, drying brown, the blades to 3 dm. long, to 7 mm. broad, scabrous on the margins and midrib, tapered to a blunt tip; involucral bracts 3-5, leaflike, unequal, the primary rays of the umbel to 10 dm. long, smooth, the small heads of 3-15 spikelets on the shorter secondary rays; spikelets yellow-brown or reddish, ovoid, 2.5-3 mm. long; scales 1-1.5 mm. long, rounded, mucronate; bristles 6, usually twice bent, about twice the length of the achene; style trifid, dark red; achene ca. 1 mm. long, light brown, broadly obovoid, mucronate.
Type locality: "In America boreali?"
Distribution: Swamps and borders of ponds; Maine, south to Georgia, west to Indiana and Kentucky.

Scirpus polyphyllus là loài thực vật có hoa trong họ Cói. Loài này được Vahl miêu tả khoa học đầu tiên năm 1805.