Plants perennial, mat-forming; rhizomes evident, sometimes vertical, long, 0.5–1.5 mm thick, soft, cortex often breaking loose, longer internodes 1–3 cm, scales fugaceous, 4–7 mm, thinly membranous, not fibrous. Culms terete, often with to 10 blunt ridges when dry, 4–60 cm × 0.3–1.8 mm, soft to firm, internally spongy. Leaves: distal leaf sheaths persistent, not splitting, proximally red (to stramineous), distally red or stramineous or green, not callose, membranous, apex usually pale red, broadly obtuse to narrowly acuminate, tooth absent. Spikelets ovoid to lanceoloid, 4–20 × 3–6 mm, apex acute; proximal scale amplexicaulous, entire; subproximal scale with flower; floral scales often spreading in fruit, 5–20, 1–2 per mm of rachilla, entirely blackish brown to red-brown, or midrib regions paler, broadly ovate, 2.5–5 × 2–2.5 mm, apex rounded to subacute, not carinate. Flowers: perianth bristles 0–6(–9), light brown to stramineous, slender to stout, often unequal, much shorter than to equaling achene; stamens 3; anthers yellow-brown to medium brown, 1.3–2.5 mm; styles 2-fid. Achenes not persistent, yellow, stramineous, or medium brown, obovoid (mostly very broadly so), thickly biconvex, angles obscure, 1–1.5(–1.9) × 1–1.6 mm, apex truncate, neck absent or very short, finely reticulate at 20–30X, or rugulose with 20 or more horizontal ridges in a vertical series, or sometimes smooth. Tubercles whitish, outline subrectangular or trapezoidal, sometimes broadly rounded, seldom pyramidal, (0.5–) 0.7–1.5 × (0.5–)0.8–1.4 mm, usually with vertical rows of depressions (cancellate). 2n = 12.
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Perennials. Rhizomes elongate. Culms 20-50 cm tall, 1.5-3 mm thick, terete, conspicuously obtusely ribbed and longitudinally sulcate, surface transversely septate when dry. Leaf sheaths 1 or 2, brownish, tubular, 6-7 cm or more, mouth slightly obliquely truncate, apex triangular mucronate. Spikelet ovoid to narrowly ovoid, 8-20 × 3-5 mm, many flowered, apex obtuse. Basalmost glume empty, amplexicaul for more than 1/2 of spikelet base; fertile glumes pale blood-red to straw-colored and ± with pale blood-red lines, tightly imbricate, oblong to ovate-oblong, ca. 4 × 1 mm, midvein obscure, margin broadly to narrowly hyaline, apex obtuse. Perianth bristles 4 or 5 but sometimes rudimentary or absent, slightly shorter than to as long as nutlet, densely retrorsely spinulose. Stigmas 2. Nutlet at first yellow then becoming tawny, obovoid, broadly obovate, or subglobose, 1-1.5 × ca. 1 mm, biconvex, smooth and shiny; persistent style base ovoid to mitriform, large, cellular spongy, 2/3 or more as long and nearly as wide as nutlet. Fl. and fr. Jul-Oct. 2n = 38-40, 44, 56.
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