Sp. Pl. 1: 328. 1753.
Herbs, annual, cespitose, 0.5–4 dm. Culms 1–many, occasionally becoming decumbent. Cataphylls 0–2. Leaves basal and cauline; auricles rudimentary or absent; blade flat, 3–13 cm × 0.3–1.1 mm. Inflorescences loose and diffuse or less often compact, usually at least ½1/2 total height of plant; primary bract shorter than inflorescence. Flowers: bracteoles 2; tepals greenish, lanceolate, 3.8–7(–8.5) mm; inner series slightly shorter, apex sometimes obtuse; stamens 3–6, filaments (0.7–)1–1.8 mm, anthers 0.3–0.8 mm; style 0.1–0.2 mm. Capsules tan to reddish brown, 3-locular, ellipsoid to narrowly so, slightly truncate, 2.7–4 × 1–1.5 mm, sometimes exceeding inner tepals but usually not outer series. Seeds yellowish, widely ellipsoid to ovoid, 0.26–0.49, not tailed. 2n = 27–37, 58–81, 108–115.
Phenology: Flowering and fruiting spring–early fall.
Habitat: Moist soils in meadows, along lakeshores or stream banks, ditches, or roadsides, especially frequent in drawdown areas, usually in open sites and often becoming weedy
Greenland, Alta., B.C., Man., N.B., Nfld. and Labr., N.W.T., N.S., Ont., P.E.I., Que., Sask., Yukon, Ala., Alaska, Ariz., Ark., Calif., Colo., Conn., Del., D.C., Fla., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo., nearly worldwide.
Nearly worldwide, Juncus bufonius is found essentially throughout North America except north of the Alaskan and Canadian tTaiga. Juncus bufonius is a highly polymorphic complex that is poorly understood systematically. Insufficient evidence exists upon which to base the segregation of the plethora of taxa that have been recognized out of this group in the past.