Plants with creeping rhizomes 0.5-1 mm thick. Culms 3-42 cm × 0.3-0.6 mm. Leaves: distal leaf sheaths often disintegrating, thinly membranous-translucent, inflated distally, often wrinkled, apex blunt. Spikelets ellipsoid, 1.5-9 × 1-3.5 mm, apex acute to acuminate; proximal scale without flower, not amplexicaulous; floral scales to 65, 5-7 per mm of rachilla, loosely appressed to appressed, elliptic, 1-3 × 0.4-1.6 mm, membranous, apex acute. Flowers: perianth bristles (0-)5-8, typically 7, white to stramineous, spinules dense to few; styles 2-fid, rarely 3-fid. Achenes stramineous to green or dark brown, biconvex, rarely trigonous, obovoid to obpryiform, 0.4-1.1 × 0.3-0.8 mm, very finely reticulate at 40X. Tubercles whitish to stramineous or green, 0.2-0.7 × 0.2-0.4 mm, apex acute to acuminate.
The varieties of Eleocharis flavescens are difficult to delimit, especially in the south, and identifications of some specimens to variety are problematic.
Tufted perennial from a compact system of slender rhizomes; stems divaricate, 3-15 cm; sheaths tenuous, pale, prolonged into a loose, white, scarious tip; spikelet ovoid or oblong-ovoid, 2-7 mm, with fewer than 20 fls; scales ovate or elliptic, obtuse or subacute, with brown sides, the basal one empty; bristles white or pale green; anthers 0.7-1 mm; style bifid or occasionally some trifid; achene lenticular, 1 mm; tubercle pale, short-conic above a swollen base. Var. flavescens, with the largest scales ca 2 mm, the tubercle a fifth as long as the black or purplish-brown achene, and the bristles usually shorter than the achene, is mainly tropical, extending n. chiefly on the coastal plain to Va. and reputedly N.J. (E. flaccida; E. ochreata) Var. olivacea (Torr.) Gleason, with the largest scales ca 2.5 mm, the tubercle a fourth as long as the olivaceous achene, the bristles usually exceeding the achene, occurs from N.S. to Minn., s. chiefly in the e. states to Fla. (E. olivacea)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.