5. Rhynchospora macrostachya Torrey ex A. Gray, Ann. Lyceum Nat. Hist. New York. 3: 206. 1835.
Ceratoschoenus macrostachyus (Torrey ex A. Gray) A. Gray; Rhynchospora macrostachya var. colpophylla Fernald & Gale
Plants perennial, cespitose, 80–150(–170) cm, coarse; rhizomes absent. Culms stiffly erect, leafy, triangular, multiribbed. Leaves ascending, overtopped by inflorescence; blades flat proximally, 3–10(–15) mm wide, apex attenuate, trigonous. Inflorescences terminal and axillary, narrow, clusters of corymbs, clusters dense, mostly broadly turbinate, 13–15 mm; bracteal leaves mostly exceeding subtended compounds. Spikelets brown, lanceoloid, 13–15 mm, apex acuminate; fertile scales lanceolate, 10–13 mm, apex acuminate, midrib short excurrent. Flowers: longer perianth bristles usually fully 2 times length of fruit body, antrorsely barbellate. Fruits 1–2 per spikelet, 20–25 mm; body pyriform obovoid, compressed, 5–6 × 2.6–3.6 mm; tubercle attenuate, 2-grooved, (15–)18–20(–21) mm. 2n = 18.
Fruiting summer–fall. Acidic sunny wetlands, mostly pond shores, seeps, bogs, marshlands; 0–400 m; Ala., Ark., Conn., Del., D.C., Fla., Ga., Ind., Kans., Ky., La., Maine, Md., Mass., Mich., Mo., N.J., N.Y., N.C., Okla., R.I., S.C., Tenn., Tex., Va.
Rhynchospora macrostachya is quickly distinguished from other species of its complex by more compact clusters, arranged on successive mid and distal nodes to present a narrow inflorescence outline. Its perianth bristles and fruit tubercles are the longest in the complex, probably in the entire genus.