Plants perennial, clonal, 50-100 cm; rhizomes slender, scaly, to 2 mm thick. Culms stiffly erect, leafy, triangular, multiribbed. Leaves erect, distal ones overtopping inflorescence; principal blades flat proximally, trigonous distally, 3-10 mm wide, apex attenuate. Inflorescences terminal and axillary, clusters of corymbs (1-)2-3, open, spikelet clusters loose; bracteal leaves mostly overtopping corymbs. Spikelets pale red brown, narrowly lanceoloid, (9-)11-14 mm, apex acuminate; fertile scales lanceolate, 9-13 mm, apex acuminate, midrib short excurrent or not. Flowers: perianth bristles 5-6, extending at least 5 mm beyond tubercle base, antrorsely barbellate. Fruits 1-2 per spikelet, 15-20 mm; body stipitate, obovoid to oblong, compressed, 4-5 × 2-3 mm, margins thick; surfaces concave, horizontally finely striate, minutely cancellate; tubercle stout based, grooved, subulate, 10-15 mm, setulose. Fruiting summer-fall. Emergent in shallows of savanna ponds, interdunal pools; 0-100 m; Ala., Del., Fla., Ga., La., Md., Mass., Miss., N.J., N.Y., N.C., R.I., S.C., Va. Rhynchospora inundata is largely confined to lower Coastal Plain terraces, mostly along the present coast. Typical plants have narrow fruit bodies and narrow inflorescences of sparse clusters, well overtopped by leaves and erect leafy bracts. By contrast, plants of R. careyana have broader fruits, shorter perianths, and larger, broader inflorescences that overtop most or all leaves and bracts. In general, plants of R. careyana are more robust and grow in more acid sites than those of R. inundata. Southward in the Atlantic Coastal and Gulf Coastal plains are broad areas of ecotone where the two species intergrade.
Much like no. 4 [Rhynchospora macrostachya A. Gray], often smaller and more slender, and producing long, coarse, stoloniform rhizomes; main lvs mostly 4-7 mm wide; infl diffusely branched; spikelets usually divergent or even reflexed, solitary or in glomerules of 2-6; bristles 8-12 mm; achenes 3.5-4.5 mm, the beak 14-19 mm. Swamps and pond-margins; e. Mass. to Del.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.