Fimbristylis autumnalis (L.) Roem. & Schult.

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.

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.

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.

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

Fimbristylis autumnalis (L.) R. & S. Syst. 2: 97. 1817
Scirpus autumnalis L. Mant. 180. 1771. (Virginia.)
Scirpus mucronulatus Michx. Fl. Bor.-Am. 1:31. 1803. (Carolina mountains.)
Scirpus Michauxii Pers. Syn. Pl. 1 : 68. 1805. (Renaming of Scirpus mucronulatus Michx.) Trichelostylis geminata Nees, Linnaea 9: 290. 1834 (nomen nudum); Lindl. & Nees; Nees in
Mart. Fl. Bras. 2' : 79. 1842. Trichelostylis ttutcronulatiis Torr. Ann. Lye. N. Y. 3: 355. 1836. Fimbristylis Frankii Steud. Syn. Cyp. 111. 1855. (Ohio.) } Finibristylis microstachya Steud. Syn. Cyp. 113. 1855. (Brazil, Pohl.) Fimbristylis autumnalis Q gracilis Boek. Linnaea 37 : 39. 1871. Trichelostylis borealis Wood, Bot. & Fl. ed. 1871. 364. 1871. (Illinois, /. IVolf.) Fimbristylis Frankii var. brachyactis Fernald, Rhodora 11: 180. 1909. (Maine.) Fimbristylis autumnalis i. brachyactis Blake, Rhodora 20: 25. 1918. ? Fimbristylis autumnalis var. gracilis Kiikenth. Repert. Sp. Nov. 23: 196. 1926. (IVilldenoiv
1226, from the Orinoco.) Fimbristylis autumnalis var. mucromilata Fernald, Rhodora 37 : 398. 1935.
Cespitose glabrous annual; culms 1-4 dm. high, narrow, 0.5-1.0 mm. wide, diffuse or erect ; leaves flat, 0.5-2.5 mm. wide ; the bracts usually shorter than the decompound to nearly simple umbel ; spikelets ovoid to narrowly cylindric, sessile or peduncled ; scales ovatelanceolate, appressed, dull brown with a greenish keel, mucronate ; achenes obovate, 0.5 mm. long, the angles often costulate, translucent buff, smooth to faintly reticulate with horizontal cells (frequently verrucose at the base, sometimes throughout) ; style terete, not fimbriate, bulbous at the base, 1.0 mm. long below the 3 branches; stamens 1 or 2, the anthers 0.3 mm. long.
Type locality: Virginia {Clayton).
Distribution : Maine, west to Ontario and Minnesota, south to Florida, Oklahoma, and Texas; British Honduras (Schipp 903, Gentle 1961); Cuba.

Fimbristylis autumnalis là loài thực vật có hoa trong họ Cói. Loài này được (L.) Roem. & Schult. mô tả khoa học đầu tiên năm 1817.