in J. J. Roemer et al., Syst. Veg. 2: 149. 1817.
Plants perennial; rhizomes 2–4 mm thick, firm, longer internodes 3–7.5 cm, scales 5 mm, tubers absent. Culms terete, 45–100 cm × (3.2–) 5–9.4 mm, soft to firm, sometimes septate-nodulose proximally, not distally, internally hollow with complete transverse septa, closer together near the spikelet, evident externally; plants never forming filiform, flaccid culms. Leaves: distal leaf-sheaths persistent, membranous to thinly papery, apex acute to acuminate. Spikelets not proliferous, (20–) 40–62 × 4–7 mm; rachilla joints bearing prominent winglike remnants of floral scales; proximal scale empty, amplexicaulous, (3–) 3.5–5 mm; floral scales 115–220, 1–3 per mm of rachilla, stramineous to pale-brown, usually with pale to dark-brown submarginal band, midrib region sometimes greenish, obovate to broadly oblong, (4–) 4.5–5 × 2.8–4 mm, cartilaginous, often membranous toward margins, margins broadly translucent, membranous, apex rounded to subacute. Flowers: perianth bristles 6–8, stramineous, stout, flattened, subequal, exceeding achene, to 2.9 mm, coarsely spinulose; anthers stramineous to reddish, 2.5–5 mm; styles 2-fid or 3-fid. Achenes stramineous to golden-yellow or reddish-brown or gray, obovoid to obpyriform, biconvex or nearly planoconvex, often with abaxial longitudinal ridge, 1.4–1.8 (–2) × 1.1–1.4 mm, markedly sculptured at 10–15X, each face with 23–37 rows of transversely elongated cells, the longitudinal walls separating the cells often prominent, apex with short neck 0.7–0.8 mm wide. Tubercles dark-brown, lamelliform, slightly higher than wide, 0.7–1.1 × 0.5–0.7 mm.
Phenology: Fruiting late spring–winter.
Habitat: Fresh ponds, lakeshores, marshes, springs, ditches, canals
Elevation: 10–500 m
Fla., Okla., Tex., Mexico, Central America, e South America
Contrary to statements in the literature, sectioning reveals that the culm septa are closer together near the spikelet than in the rest of the culm in both Eleocharis interstincta and E. equisetoides.