Keeled Lateral Bulrush

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.