Cyperus amplissimus Steudel

Herbs, perennial; rhizomes 3–20 cm × 1–2 cm, indurate. Culms stoutly trigonous, thickened, 50–300 cm × 5–30 mm, basally indurate, glabrous. Leaves V-shaped, with cross ribs, 40–130 cm × 10–15 mm, margins and keel scabrid. Inflorescences: spikes appressed-ascending, narrowly cylindric, (2–)3–45 mm × (4–)7–10 mm; rays (5–)9–12, 2–22(–30) cm; 2d order rays distinctly flattened, 1–10 cm; 3d order rays flattened, 0.5–3 cm; rachis 2.5–4 cm; bracts (6–)9–10, ascending at 45–75°, V- or inversely W-shaped, (5–)15–90 cm × 0.5–20 mm; rachilla persistent, wings 0.2–0.4 mm wide. Spikelets (4–)10–35, appressed-ascending, compressed, linear, 7–12(–15) × 0.6–1.2 mm; floral scales deciduous, 6–20, marginally clear, laterally brown, medially green, laterally 2–3-ribbed, medially 1-ribbed, oblong-ovate, (3.2–) 3.8–4.3 × 1.2–1.7 mm, apex spreading, acute to obtuse, mucronulate. Flowers: anthers 0.7–0.9 mm, connective apex bright red, oblong, to 0.1 mm; styles 0.8–1.3 mm; stigmas 2–3.3 mm. Achenes brown, sessile, narrowly ellipsoid, 1.8–2.5 × 0.8–1.3 mm, apex ± acute, not apiculate, surfaces puncticulate.

Fruiting summer. Coastal marshes; 0–10 m; La.; Mexico; Central America; South America.

Cyperus prolixus produces large plants, similar in habit to C. giganteus and C. papyrus but easily distinguished by flattened rays.