Sketch Bot. S. Carolina 1: 62. 1816.
Plants perennial, cespitose, 70–150 cm; rhizomes often present, short, scaly. Culms erect or ascending, leafy, trigonous. Leaves exceeded by culm; blades linear, proximally 4–7 mm wide, apex trigonous, tapering. Inflorescences terminal and axillary; clusters 3–6, mostly dense, narrowly to broadly turbinate, branches ascending; leafy bracts exceeeding proximalmost inflorescences. Spikelets rich brown, ovoid, (3–)4–5 mm, apex acuminate; fertile scales ovate, 2.5–3.5 mm, apex acuminate, midrib included or shortexcurrent. Flowers: perianth bristles mostly 6, exceeding tubercle tip. Fruits mostly 3–4 per spikelet, 2–2.2 mm; body brown on short pedicellar (to 0.3 mm) stalk, broadly obovoid, lenticular, 1.3–1.5 × 1–1.5 mm, surfaces transversely rugulose, vertically finely striate and rectangularalveolate; tubercle compressed, triangular acuminate, 0.5–0.8 mm, edges setulose.
Phenology: Fruiting summer–fall.
Habitat: Low meadows, clearings, marshes, marsh borders, seeps, bog moats, savannas, ditches, pine flatwoods, swamps
Elevation: 0–400 m
Ala., Ark., Fla., Ga., La., Miss., N.C., Okla., S.C., Tenn., Tex., Va.
Rhynchospora caduca has its closest relationships with the even more robust R. odorata Grisebach, on the one hand, and the swampinhabiting, more slender, and rhizomatous R. mixta Britton ex Small, on the other. Intergrades with R. odorata appear in Alabama and northwest Florida; intergrades with R. mixta appear where ranges overlap in both the Atlantic and Gulf coastal plains.