Plants perennial, densely cespitose; rhizomes concealed by persistent culm bases, short, 4-5 mm thick, hard, cortex persistent, internodes crowded, scales decaying to coarse fibers, 1 cm, papery. Culms greatly compressed, 4-10 times wider than thick, often with 1 or 2 sharp ridges on 1 side, (8-)20-35 cm × 0.7-2.3 mm, hard, finely striate, spongy. Leaves: distal leaf sheaths persistent, not splitting, proximally red or stramineous, distally green to stramineous, inflated, papery, apex dark brown, broadly obtuse to subtruncate, callose, tooth absent. Spikelets ovoid, 4-9 × 2.5-4 mm, apex acute; proximal scale clasping 2/3-3/4 of culm, apex 2-fid; subproximal scale empty or with a flower; floral scales spreading in fruit, 30-60, 6-9 per mm of rachilla, medium or pale brown, midrib region often paler, ovate-lanceolate, 2.5-3.5 × 1.5 mm, apex 2-fid, carinate in distal part of spikelet. Flowers: perianth bristles 0(-5), stramineous to pale brown, 1/2 of to equaling achene length; stamens 3; anthers orange-brown, 0.7-1.5 mm; styles 3-fid. Achenes falling with scales, yellow-brown to medium brown, obovoid to obpyriform, nearly equilaterally trigonous, cross section circular to slightly compressed, angles obscure or evident, 0.9-1.1 × 0.6-0.75, neck usually very short, finely rugulose at 10-30X, 20 or more low, blunt horizontal ridges in vertical series. Tubercles brown, depressed-pyramidal, often rudimentary, 0.1-0.25 × 0.2-0.3 mm.

Fruiting spring-summer (May-Jun). Seasonally wet places on limestone, cedar (juniper) glades, stream beds, prairies, ditches; 200-300 m; Ala., Ga., Ky., Tenn.

Eleocharis bifida was previously included in E. compressa. A very few specimens of E. compressa var. compressa from the states where E. bifida is known are like E. bifida except for their entire proximal floral scales and evident rhizomes.