Plants annual; rhizomes absent; roots purplish brown to black, fibrous. Culms mostly solitary or few together, stout, 60–180 cm, strongly retrorsely scabrous. Leaves: proximal sheaths purplish, winged, strongly ribbed, sparsely pubescent; contra-ligule triangular; blades linear, M-shaped in cross section, shorter than culms, 10–25 mm wide, glabrous, retrorsely scabrous on midrib, mid lateral veins, and margins. Inflorescences: axillary 2–4, terminal 1, stalked panicles, open paniculate, terminal panicle 7–14 cm with numerous short fascicles 4–8 mm wide, of 2–5 spikelets; bracts subtending inflorescence leaflike, broadly attenuate, ± equaling inflorescence, antrorsely scabrous. Spikelets bisexual and staminate, few flowered, 3.8–5 mm; staminate scales narrowly ovate, pistillate scales purple with prominent green keel, broadly ovate, abruptly acuminate. Achenes greenish to whitish or sometimes mottled gray, shiny, rounded-trigonous to ± circular, ovoid, 3.4–3.8 × 2.3–2.8 mm, smooth, apex rounded; hypogynium whitish to pale brown, bluntly 3-angled, low.
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An aquatic plant rooting at the lower nodes of the stem, with very scabrous stems, leaf-margins and leafsheaths, and branches of the inflorescence. The contraligule is semi-orbicular and bordered by a firm, brown band with a membranous appendage. The bracts subtending the clusters of spikelets are definitely longer than those in S. junghuhniana, the glumes much darker, and the nuts do not exceed the glumes.
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