Keeled Lateral Bulrush

Isolepis carinata sometimes occurs in mixed populations with the very similar I. pseudosetacea.

Plants annual; rhizomes absent. Culms 1–25 cm × 0.2–0.3 mm. Leaves: sheaths green to stramineous or brown; distal blade mostly much longer than sheath, to 5 cm × 0.2–0.5 mm. Inflorescences: involucral bract 1, 5–25(–33) mm. Spikelets 1–10 × 1.5–2 mm; scales stramineous to pale orangish, midrib region often greenish, markedly gibbous, prominently to obscurely veined, midrib keeled, finely reticulate at 20X, membranous, hyaline, apex rounded, awned; proximal scale to 2.5(–5) mm, awn to 2 mm; other scales 1.8–2 × 1–1.2 mm, awn 0.2–0.5 mm. Flowers: anthers 0.2 mm; styles 3-fid. Achenes often falling with and clasped by floral scales, dark orange-brown or often whitish, broadly ellipsoid to obovoid or outline subcircular, nearly equilaterally trigonous, faces concave, 1–1.5 × 0.7–1 mm, papillose at 10–15X, papillae in many vertical rows, often obscured by thin, minutely reticulate, whitish surface layer.

Ala., Ark., Calif., Fla., Ga., Ill., Kans., Ky., La., Miss., Mo., N.C., Okla., S.C., Tenn., Tex.

Fruiting spring.

Wet, often drying, freshwater places in grasslands, rock barrens, open woods, lawns, cultivated fields, waste places; 0–800m.

Isolepis koilolepis Steudel; Scirpus carinatus (Hooker & Arnott ex Torrey) A. Gray 1868, not Smith 1809; S. koilolepis (Steudel) Gleason

Scirpus koilolepis (Steud.) Gleason, Rhodora 44: 479. 1942.
Heleogiton trigonum Reichenb. in Mossier, Handb. ed. 2, 1807. 1829. Not H. trigonum Roth,
1802. Isolepis carinata H. & A. ; Torr. Ann. Lye. N. Y. 3 : 349. 1836. Isolepis koilolepes* Steud. Syn. Cyp. 318. 1855.
Scirpus carinatus A. Gray, Proc. Am. Acad. 7: 392. 1868. Not Scirpus carinatus Smith, 1824. Isolepis Hookeri Nees; Bock. Linnaea 36: 498, as syn. 1870. Trichelostylis carinata Wood, Class-Book ed. 1861, 742. 1861.
Annual, fibrous-rooted, cespitose; culms 0.5-5 dm. tall, terete, grooved, green, smooth, the sheaths green drying brown at the base, smooth, the margin of the orifice hyaline, truncate, the blades to 4 cm. long, smooth, blunt-tipped; involucral bract to 2.5 cm. long, single, smooth, blunt-tipped; spikelets ovate, green drying pale brown, 1-3 on a culm, to 5 mm. long, ca. 3 mm. broad, 2-12-flowered; scales ca. 2 mm. long, strongly carinate, acute, 2-3-nerved on the broadly hyaline margins, the broad, green midrib shortly mucronate, smooth; bristles absent; style trifid, brownish; achene ca. 1.5 mm. long, light to dark brown, strongly triangular with concave sides, globose in outline, constricted to a short-necked base, minutely apiculate.
Type locality: New Orleans, Louisiana.
Distribution: Swamps and moist stream banks; Georgia; Tennessee and Alabama to Oklahoma and Texas; California.

Isolepis carinata (syn. Scirpus koilolepis) is a species of flowering plant in the sedge family known by the common name keeled bulrush. It is native to North America, where it is mostly distributed around the southeastern United States; it can also be found on the California coast. It grows in many types of moist and wet habitat, including disturbed, cultivated, and landscaped areas. It is an annual herb producing clumps of slender, erect stems up to 25 centimeters tall. The inflorescence is a solitary spikelet just a few millimeters long, or a cluster of up to three spikelets. These are accompanied by a stiff bract which looks like an extension of the stem growing past the spikelets.