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 x 0.3--1.1 mm. Inflorescences loose and diffuse or less often compact, usually at least ½ 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 x 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. Flowering and fruiting spring--early fall. 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.
Annual to 3 dm, the stems terete, sometimes branched; lvs basal and usually also cauline, capillary, 0.5-10 cm נ0.2-1.1 mm, convex on the lower surface, flat or channeled on the upper; fls often cleistogamous, scattered singly along the upper part (often more than half) of the stem, short-pedicellate or subsessile in the axils of hyaline-scarious or partly leafy bracts, each one also closely subtended by a pair of broad, hyaline-scarious bracteoles 1-2.5 mm; tep slender, with greenish midstrip and hyaline margins, mostly 3-6 mm, the outer a little the longer; anthers 6, 0.3-1 mm, up to as long as the filaments; style very short, fr imperfectly trilocular; seeds 0.3-0.6 mm, apiculate; 2n=26-120, a small polyploid pillar-complex. Moist or vernally wet or moist places; nearly cosmopolitan, and throughout our range. Most of our plants are polyploid and have acuminate pet slightly longer than the fr. A ±diploid halophytic phase, found in salt-marshes along the coast from Lab. to Mass., and widespread in Europe, differs morphologically from typical, widespread J. bufonius in its consistently small size (rarely to 15 cm) and obtuse or mucronate pet equaling or slightly shorter than the fr. This phase has been segregated as var. halophilus Fernald or J. ambiguus Guss.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.