13. Rhynchospora capillacea Torrey, Fl. N. Middle United States. 1: 55. 1823.
Phaeocephalum capillaceum (Torrey) Farwell; Rhynchospora setacea (Muhlenberg) MacMillan 1892, not Vahl 1806; Triodon capillaceus (Torrey) Farwell
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.