Fimbristylis vahlii (Lam.) Link

Plants annual, cespitose, delicate, 4–15 cm, bases soft; rhizomes absent. Leaves polystichous, mostly spreading or excurved, often exceeding culms; sheaths entire, abaxially smooth or sparsely hirtellous; ligule absent; blades filiform, to 0.5 mm wide, somewhat involute, abaxially glabrous or ascending-strigillose. Inflorescences terminal; spikelets sessile or subsessile in single capitate leafy-involucrate cluster; scapes filiform; involucral bracts leafy, setaceous, greatly overtopping inflorescence. Spikelets greenish, cylindric to lanceoloid-cylindric, 5–10 mm; fertile scales narrowly ovate to lanceolate, 1–1.5 mm, acute, glabrous, midrib strong, excurrent as cusp. Flowers: stamens 1; styles 2-fid, slender, bulbous-based, smooth or papillate. Achenes pale, tumidly obovoid, 0.5–0.7 mm, cancellate, pits horizontally rectangular in 5–7 vertical rows per side. 2n = 20.

Ala., Ariz., Ark., Calif., Fla., Ga., Ill., Kans., Ky., La., Miss., Mo., Nebr., Okla., S.C., Tenn., Tex.; Mexico; Central America; South America.

Fruiting summer–fall.

Moist to wet, alluvial or mineralized banks, shores, fluctuating pond and lake edges, often a “drawdown” plant around stock tanks and reservoirs; 0–500m.

Scirpus vahlii Lamarck in J. Lamarck and J. Poiret, Tabl. Encycl. 1: 139. 1791 (as vhalii); Fimbristylis apus (A. Gray) S. Watson; F. congesta Torrey; F. vincentii Steudel; Isolepis vahlii (Lamarck) Kunth; Scirpus apus A. Gray

Fimbristylis vahlii (Lam.) Link, Hort. Berol. 1 : 287. 1827
Scirpiis Vahlii ("Vhalii") Lam. Tab. Encyc. 1: 139. 179L
Isolepis Vahlii H.B.K. Nov. Gen. & Sp. 1 : 22L 1816.
Fimbristylis congesta Torr. Ann. Lye. N. Y. 3 : 345. 1836. (New Orleans, Drummond.)
Fimbristylis Vincentii Steud. Syn. Cyp. 109. 1855. (Texas.)
Scirpiis apus A. Gray, Proc. Am. Acad. 10: 78. 1874. (California, Bolander.)
Fimbristylis apus S. Wats. Bot. Calif. 2 : 224. 1880.
Fimbristylis perpusilla Harper; Small, Fl. SE. U. S. 188. 1903. (Georgia.)
Cespitose annual with capillary culms 1-15 cm. high, or with spikelets frequently sessile at the base; leaves filiform, rough, channeled or somewhat flattened, nearly equaling the culms ; involucral bracts filiform, much exceeding the capitate clusters of 3-8 spikelets ; spikelets oblong-cylindric, obtuse, 4-8 mm. long, many-flowered ; scales oblong-lanceolate, acuminate, green to dull brown, with prominent midrib; achene obovate, 0.4 mm. long, stramineous, translucent, prominently reticulate with horizontally elongated cells ; style very slender, 0.8 mm. long, not fimbriate below the short bifurcation, bulbous at the base ; stamen
1, the anther 0.2 mm. long.
Type locality: "Habitat in America meridionali, nee in Hispania" (Vahl, Enum. 2: 263).
Distribution : In moist soil, chiefly river banks : North Carolina to Florida, west to Texas and Missouri; California; Nicaragua (C. Wright); South America.

Fimbristylis vahlii is a species of sedge known by the common name Vahl's fimbry. It is native to much of Central America and the southern half of North America, where it grows in wet habitat. This is a small, clumping sedge producing rounded stems just a few centimeters high surrounded by curling, thready leaves. At the top of the stem is an inflorescence which is a cluster of several cylindrical, pointed spikelets surrounded by long, narrow, twisting bracts. The fruit is a tiny achene about half a millimeter wide.

Fimbristylis vahlii là loài thực vật có hoa trong họ Cói. Loài này được (Lam.) Link mô tả khoa học đầu tiên năm 1827.