Culms subterete to slightly compressed, to 2 times as wide as thick, (0.2-)0.5-1 mm wide. Distal leaf sheaths often with tooth, to 0.1(-0.5) mm.
Fruiting spring-summer. Seasonally wet seeps and depressions in calcareous grasslands, meadows, open oak woods, ditches, sometimes limestone, rarely saline marsh or lakeshores; 10-2300 m; B.C., Man., Sask.; Colo., Ill., Iowa, Kans., Minn., Mo., Nebr., N.Mex., N.Dak., Okla., S.Dak., Tex.
Some specimens herein included in E. compressa var. acutisquamata are intermediate with E. elliptica in their floral scales, including the single record from British Columbia. Eleocharis compressa var. acutisquamata probably occurs in Alberta; I have not seen specimens.
Perennial herb with slender rhizomes, mat-forming 8 - 45 cm tall Leaves: reduced to bladeless sheaths, basal, two per culm, margins fused and enclosing culm, not splitting, red basally, reddish brown at the apex, papery, with a blunt to nearly truncate (cut straight across) apex that often bears a tiny tooth. Flowers: minute, spirally arranged on the axis of the spikelet, lacking sepals and petals, with zero to five bristles, subtended by a scale. Bristles (when present) straw-colored, equal to or shorter than the achene. Stamens three, exserted. Anthers orangish brown to yellow, to 2 mm long. Pistil one. Style three-cleft, or some two-cleft. Fruit: a one-seeded achene, yellowish brown to dark brown, 1 - 1.5 mm long, to 0.8 mm wide, reverse egg-shaped to reverse pear-shaped, three-angled (nearly equilaterally to compressed), some convex on both sides, finely wrinkled, sometimes finely latticed. Tubercle brown to whitish, tiny, pyramidal, often depressed. Seed with a thin, non-adherent wall. Culm: unbranched, 8 - 45 cm long, 0.5 - 1 mm wide, nearly circular in cross-section or slightly compressed to two times as wide as thick, often twisted, two- to twelve-ridged, spongy, enclosed basally by two fused sheaths. Spikelets: solitary, 4 - 8 mm long, 2 - 4 mm wide, egg-shaped with a pointed apex, with 20 to 60 floral scales. Scales spirally arranged and overlapping, brown to dark brown with a paler midrib, sometimes colorless or straw-colored, hyaline towards the apex, 2 - 3 mm long, 1 - 1.5 mm wide, egg-shaped with a pointed apex, some becoming two-cleft or torn-looking with age.
Similar species: No information at this time.
Flowering: late April to mid-June
Habitat and ecology: Occasional, especially in the southwestern sector of the Chicago Region. Found in moist to mesic areas of calcareous prairies.
Occurence in the Chicago region: native
Etymology: Eleocharis comes from the Greek words heleios, meaning "dwelling in a marsh," and charis, meaning grace. Compressa means compressed.