Small Fruit Spike Rush

Specimens of Eleocharis brittonii and E. microcarpa without achenes are often difficult to distinguish. More detailed study of the four apparent entities across the two species is warranted.

Plants usually annual, tufted, sometimes mat-forming via proliferating and arching inflorescences (stoloniferous), sometimes entirely vegetative; rhizomes absent. Culms often ascending or arching, quadrangular or broadly elliptic, 2–40 cm × 0.1–0.4(–0.6) mm, soft. Leaves: distal leaf sheaths persistent or disintegrating, pale brown, green or red-brown, streaked or mottled red-brown or purple, translucent, membranous, apex narrowly acute. Spikelets: basal spikelets absent; often proliferous, ovoid to ellipsoid or lanceoloid, terete, 2–10.7 × 1–2 mm, apex acute; proximal scale empty, persistent, amplexicaulous, dissimilar to floral scales, often longer, often resembling an involucral bract, ovate to lanceolate, midrib markedly thickened and broad and often prolonged beyond lamina; subproximal scale with flower; floral scales spiraled, colorless, whitish, or pale brown, streaked or mottled red-brown or purple, midribs green and red-brown or green and purple, ovate to elliptic, 0.8–1.5 × 0.4–0.8 mm, membranous, midrib obscure to prominent. Flowers: perianth bristles present or sometimes apparently absent; stamens 3; anthers 0.15–0.35; styles 3-fid. Achenes whitish to olive or pale brown, sometimes spotted olive or red-brown, obovoid, trigonous (or subterete), angles prominent, 0.55–0.8 × 0.3–0.5 mm, apex constricted proximal to tubercle, smooth. Tubercles green or pale brown to red-brown, trigonous.

Eleocharis microcarpa Torr. Ann. Lye. N. Y. 3 : 312. 1836
Eleocharis microcarpa 0? filiculmis Torr. Ann. Lye. N. Y. 3 : 312. 1836. (New Jersey.) Heleocharis Torreyana Bock. Linnaea 36: 440. 1870. Heleocharis cuhensis Bock. Beitr. Cyp. 2: 10. 1890. (Cuba.)
Annual ; culms 1-3 dm. high, finely capillary, flexuous, often quadrangular-sulcate ; roots fibrous, white ; sheaths inconspicuous, closely investing the culm, purple-striate at the base, somewhat acuminate at the apex ; spikelets many-flowered, oblong to ovate, 2-7 mm. long ; stamens 2 or 3; style trifid; scales loose, strongly keeled, especially toward the acuminate apex, ovate, with a whitish margin and green, red-bordered midrib, all deciduous except the enlarged lowest scale, which persists as a bract; achene minute, 0.6-0.7 mm. long (nearly 0.7 mm. in the type), obovate, triangular, pale gray or yellowish, smooth; style-base shortpyramidal, gray, often reddish when young; bristles whitish to light brown, appressed, less than half the length of the achene.
Type locality: New Orleans (Ingalls).
Distribution: Connecticut; New Jersey to Florida and Texas, mostly near the coast; Tennessee and Indiana.

Eleocharis microcarpa, common names small-fruited spikesedge, spike-rush, small-fruited spike-rush and tiny-fruited spike-sedge, is a plant in the Eleocharis genus found in North America.