Plants perennial, cespitose, 10-40 cm, wiry; rhizomes stoloniferous, slender, to 1.5 mm thick. Culms erect or curved, leafy, filiform, angularly few ribbed. Leaves ascending-excurved, overtopped by culm; blades filiform, involute, apex setaceous. Inflorescences: spikelet clusters 1-2(-3), often sparse, ellipsoid or narrowly turbinate, less than 1 cm wide; subtending foliaceous bracts exceeding compounds. Spikelets erect or ascending, pale red brown to brown, fusiform, 6-7 mm; fertile scales elliptic, 4 mm, apex rounded or acute, midrib short excurrent or not. Flowers: perianth bristles 6, overtopping tubercle base, mostly retrorsely barbellate, sometimes smooth [forma laeviseta (E. J. Hill) Fernald]. Fruits 1-4(-5) per spikelet, 2.5-3 mm; body pale brown, slender stipitate, ellipsoid, lenticular, 1.5-2 × 0.8-1 mm; surfaces longitudinally minutely striate, obscurely transversely low rugose, dotted; tubercle narrowly triangular subulate, flattened, 0.8-1.7 mm. Fruiting summer-fall. Moist to wet calcareous fens, seeps over limestones or calcareous rock, marsh meadows; 0-1000 m; Alta., Man., N.B., Nfld. and Labr., Ont., Que., Sask.; Ala., Ark., Conn., Ill., Ind., Iowa, Maine, Mass., Mich., Minn., Mo., N.H., N.J., N.Y., N.Dak., Ohio, Okla., Pa., R.I., S.Dak., Tenn., Tex., Vt., Va., Wis. The two beakrushes most commonly occurring in fens are Rhynchospora capillacea and R. capitellata.
Cespitose; lvs involute, filiform, 0.2-0.4 mm wide; glomerules 1 or commonly 2, the terminal ovoid or oblong, with 2-10 erect or ascending spikelets, the lateral remote, subsessile, with 1-4 spikelets; bristles 6, retrorsely barbellate or seldom smooth, surpassing the achene; achenes elliptic- oblong to narrowly elliptic-obovate, 1.7-2.1 mm, scarcely (or less than) half as wide, conspicuously narrowed toward the base, pale (and often obscurely darker-lined) centrally, darker toward the margins; tubercle subulate- attenuate, 0.8-1.6 mm; 2n=26. Calcareous swamps, bogs, and shores; Nf. to Sask., s. to Va., Tenn., and Mo.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.