Plants annual, cespitose or solitary, (10–)20–100 cm; rhizomes absent. Culms erect, leafy, nearly terete or angled, many ribbed. Principal midculm leaves often exceeding inflorescences; blades linear, proximally flattened, 1–5 mm wide, apex trigonous, tapering. Inflorescences terminal and axillary, clusters of corymbs 1–5, usually diffuse; leafy bracts exceeding proximal corymbs. Spikelets dark brown, lanceoloid to ovoid, mostly 4–6(–8) mm, apex acute; fertile scales many, ovate, rounded-convex, 2–3.5 mm, apex acute, midrib mostly included, rarely forming apiculus. Flowers: perianth absent. Fruits 1–1.3(–1.5) mm, body dark brown, tumidly lenticular, nearly orbicular, 0.7–1 × 0.7–1 mm, margins strong, interrupted at tubercle base; surfaces irregularly transversely rugulose with wavy rows of vertical, linear, raised cells; tubercle depressed-triangular, 0.1–0.3 mm, capping fruit summit, base broadly 2 lobed.
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Much like no. 1 [Rhynchospora scirpoides (Torr.) Griseb.]; achene scarcely stipitate, transversely conspicuously rugose, only inconspicuously margined; tubercle very short and closely appressed. Wet sandy soil and bogs; se. Mass. to Tex.; nw. Ind. (Psilocarya n.)