15. Fimbristylis autumnalis (Linnaeus) Roemer & Schultes in J. J. Roemer et al., Syst. Veg. 2: 97. 1817.
Scirpus autumnalis Linnaeus, Mant. Pl. 2: 180. 1771; Fimbristylis autumnalis var. mucronulata (Michaux) Fernald; F. frankii Steudel; Scirpus michauxii Persoon; S. mucronulatus Michaux; Trichelostylis geminata T. Lestiboudois & Nees; T. mucronulata (Michaux) Torrey
Plants annual, cespitose, 5–20(–30) cm, glabrous, plant base soft; rhizomes absent. Leaves distichous, shorter or longer than culms; sheaths keeled, entire or distally ciliate; ligule of short hairs complete; blades narrowly linear, 1–3 mm wide, flat, margin scabrid-ciliate. Inflorescence: anthelae compound, mostly diffuse, mostly turbinate, as broad as long, ascending-branching; scapes filiform to linear, distally variously compressed, sometimes alate, 0.5–1.5(–2) mm wide, edges scabrid; primary involucral bract usually 1, blade exceeding or exceeded by anthela. Spikelets red-brown or brown, mostly narrowly lanceoloid to narrowly ellipsoid, 3–7 mm; fertile scales lanceolate, keeled, 1.5–2 mm, narrowly acute, glabrous, midrib excurrent as mucro. Flowers: stamens (1–)2; styles 3-fid, slender, with 3 angled base, glabrous. Achenes pale brown, trigonous-obovoid, 0.5–0.7 mm, apiculate and 3-ribbed, smooth to variably warty. 2n = 10.
Fruiting summer–fall, all year southward. Moist to wet sands, peats, silts, or clays, primarily of disturbed, sunny ground such as seeps, ditches, savanna, stream banks, reservoir drawdowns, and pond shores; 0–500(–1000) m; N.B., Ont., Que.; Ala., Ark., Conn., Del., D.C., Fla., Ga., Ill., Ind., Iowa, Kans, Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Nebr., N.H., N.J., N.Y., N.C., Ohio, Okla., Pa., R.I., S.C., S.Dak., Tenn., Tex., Vt., Va., W.Va., Wis.