Plants perennial; rhizomes evident, 1 mm thick, firm, cortex unknown, internodes unknown, scales fugacious, 5 mm, membranous. Culms terete, often with a few blunt ridges when dry, 20-50 cm × 0.2-0.7 mm, soft, spongy. Leaves: distal leaf sheaths persistent, not splitting, proximally red or stramineous, distally green, membranous, apex usually reddish, subtruncate to obtuse, not callose, tooth present, to 0.4 mm. Spikelets narrowly lanceoloid, narrowly ovoid, or narrowly cylindric, 4-10 × 1-1.5 mm, apex narrowly acute; proximal scale amplexicaulous or clasping 3/4 of culm, entire; subproximal scale empty or with flower; floral scales spreading in fruit, 20-80, 5-6 per mm of rachilla, orange-brown, midrib regions stramineous, narrowly ovate-lanceolate, 1.5-2 × 0.8 mm, entire, apex acute, not carinate. Flowers: perianth bristles 3-6, stramineous, stout, unequal, rudimentary to less than 1/2 achene length; stamens 3; anthers stramineous, 0.7-1.4 mm; styles 3-fid. Achenes falling with scales, stramineous, ellipsoid, compressed-trigonous, angles prominent (keeled), 0.6-0.65 × 0.4-0.45 mm, base narrowed, neck long, smooth at 40X. Tubercles brown, pyramidal, as high as wide to greatly depressed, 0.1-0.25 × 0.15-0.2 mm.

Fruiting spring-summer. Ephemeral pools in old rock quarry; 300 m; Tex.; South America (Argentina, Paraguay).

Eleocharis cylindrica is synonymous with E. spegazzinii Barros, which was described from temperate South America (E. R. Guaglianone and O. Ueno 1990). It is very uncommon in North America, where it has been confirmed from Aransas, Burnet, and Cameron counties in Texas; reports from Lubbock and Presidio counties have not been confirmed. The report from New Mexico cannot be confirmed because the specimens lack achenes.