Plants perennial, to 150(-200) cm, cespitose or not; rhizomes scaly, slender, elongate. Culms wand-like, at least 50 cm. Leaves nearly distichous, spreading to ascending, 1/2 length of culms, sheath margins ciliolate at junction with blade, backs smooth to pubescent; ligule present, usually complete; blades linear, 2-5 mm wide, flat to involute, margins scabridulous, surfaces mostly glabrous. Inflorescences: anthelae compound, dense or diffuse, mostly longer than broad; scapes wandlike, broadly linear, distally usually compressed, marginal ribs scabrid distally; longest primary involucral bract exceeding or shorter than anthela. Spikelets pale brown or red-brown, broadly ovoid, ellipsoid, or lanceoloid, 5-15 mm; fertile scales ovate, 3-4 mm, apex rounded, often puberulent distally, midrib excurrent as scabrid mucro or short cusp. Flowers: stamens 3; styles 2-fid, flat, fimbriolate. Achenes pale to deep brown, lenticular-obovoid, 1 mm, finely but definitely cancellate with 14-15 horizontally oriented lattices per side. 2n = 20, 30, 60. Fruiting summer-fall. Sands or sandy peats of slightly brackish to circumneutral marsh, interdunal swales and low sandy areas near coast; 0-100 m; Ala., Del., Fla., Ga., La., Md., Miss., N.J., N.C., S.C., Tex., Va.; Mexico; West Indies. The tallest, coarsest plants of Fimbristylis caroliniana, formerly referred to as F. harperi Britton ex Small, are the most clonal of North American Fimbristyloids, some clones literally covering acres of sandy swale or beach.
Perennial from long, slender rhizomes; stems solitary or in small tufts, to 1.5(-2) m, tending to be flattened and scabrous-edged above; lvs subdistichous, mostly 2-5 mm wide, scabrous on the margins distally, usually otherwise glabrous; ligule a line of short hairs; longest invol bract from much shorter to slightly longer than the infl; spikelets 5-15 mm, ellipsoid or lance-ovoid, few-many in a compound system of subumbellate cymes, the edges of the peduncles scabrous; scales ovate, glabrous or often puberulent distally, sometimes shortly excurrent-mucronate; stamens 3; anthers ca 3 mm; style bifid, fimbriate from near the base to just above the branch-point; achene lenticular, obovate, 1 mm, finely cellular-reticulate in vertical rows; 2n=20, 40, 60. Coastal marshes and dune-swales, or sometimes farther inland on the coastal plain, landward from no. 5 [Fimbristylis castanea (Michx.) Vahl ], seaward from no. 4 [Fimbristylis puberula (Michx.) Vahl]; N.J. to Fla. and Mex.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.