Plants perennial, cespitose, to 50 cm; rhizomes absent. Culms erect to arching, leafy, linear to filiform, nearly triangular. Leaves ascending, overtopped by culm; blades flat, linear to filiform, to 1.8 mm wide, apex distally involute, trigonous, setaceous. Inflorescences terminal and axillary, spikelet clusters 2-4, widely spaced, the lowest near plant base; clusters compact, broadly turbinate to hemispheric, to 1.5 cm wide; leafy bracts curved, setaceous, slightly to greatly overtopping subtended compounds. Spikelets dark brown, lance-ellipsoid, 2-3 mm; fertile scales 2 mm, apex acute, midrib short-excurrent or not. Flowers: perianth bristles 6, ± as long as fruit body, retrorsely barbellate. Fruits mostly 2 per spikelet, 1.5-1.9 mm; body brown with yellowish center, ellipsoid, lenticular distal to short stipe, 1-1.3 × 0.6-0.8 mm; tubercle triangular, 0.3-0.6 mm, distinctly shorter than fruit body. Fruiting summer-fall. Moist to wet pine barrens, sand pits, borrow pits; of conservation concern; 0-100 m; Del., N.J. Rhynchospora knieskernii is in the Center for Plant Conservation´s National Collection of Endangered Plants.
Cespitose perennial to 5 dm; stems slender, flexuous; lvs 1-2 mm wide, soon becoming involute; terminal glomerule turbinate, 5-10 mm thick; lateral glomerules 2 or 3, remote, somewhat smaller, subsessile; spikelets 2-3 mm, brown, with 2-3 frs and a terminal staminate fl; bristles 6, retrorsely barbellate, half to fully as long as the achene; achenes plump, elliptic or obovate, 1.1-1.3 mm, slightly or scarcely more than half as wide, obscurely roughened, shining yellow-brown centrally, darker toward the margins; tubercle triangular, up to half as long as the achene. Pine-barren bogs; N.J. to Del.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.