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 short excurrent. 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 rectangular alveolate; tubercle compressed, triangular acuminate, 0.5-0.8 mm, edges setulose.
Fruiting summer-fall. Low meadows, clearings, marshes, marsh borders, seeps, bog moats, savannas, ditches, pine flatwoods, swamps; 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 swamp inhabiting, 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.
Stout, erect, 7-11 dm, the stems loosely clustered on short rhizomes; lvs flat, to 7 mm wide; infl elongate, of several peduncled, loosely branched, broadly turbinate or corymbiform cymes; spikelets ovoid, 4-6 mm, dark brown, with 3-6 fls and 2-5 frs; bristles 6, brittle, antrorsely barbellate, surpassing the tubercle; achenes light brown, broadly obovate to subrotund, 1.3-1.6 mm, nearly or quite as wide, transversely sharply ridged; tubercle acute, 0.4-0.7 mm. Marshes and wet soil, chiefly on the coastal plain; se. Va. to Fla. and Tex.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.