Herbs annual, scandent, 0.3-2 m tall. Stem light green to green, often becoming reddish purple at maturity, simple to extensively branched, glabrous, angulate, with recurved prickles along angles, often decumbent at base, usually producing fibrous roots at lower nodes. Leaves petiolate, upper ones often shortly petiolate or subsessile; petiole 0.5-4 cm, glabrous, retrorsely prickly along angles; leaf blade green adaxially, light green abaxially, broadly lanceolate to oblong, 2-8.5 × 1-3 cm, thin, abaxially glabrous, abaxially usually retrorsely prickly near base of midvein, adaxially glabrous to densely pubescent with appressed simple multiseriate hairs, base sagittate to deeply cordate with small rounded or triangular lobes, margin ciliate or eciliate, apex acute to subacute or obtuse; ocrea oblique, 0.5-1.3 cm, scarious, glabrous, often weakly ciliate at tip, lower ones often lacerate. Inflorescence terminal or in axils of upper leaves, elongate, 3-15 cm, often slender, usually branched, usually glabrous but sometimes with a few recurved prickles in lower portion; inflorescence bracts resembling ocrea but much reduced, 1.5-3 mm; each inflorescence branch terminated by a dense headlike cluster of many flower fascicles. Flower fascicles usually 2- or 3-flowered, closely spaced; bracts lanceolate to narrowly elliptic, 3-5 mm, glabrous, apex strongly acuminate; bracteoles narrowly elliptic to elliptic, 3-4 mm, glabrous, often ciliate at tip; pedicel short, 1-1.5 mm, glabrous, included in bracteoles. Perianth white to greenish white, often reddish, 3-5 mm, 5-parted; tepals broadly elliptic, not becoming fleshy, apex obtuse. Stamens 8, inserted at base of perianth in 2 whorls; inner stamens 3, ca. 2 mm; outer stamens 5, 1-1.5 mm. Style 1, 3-cleft to middle, ca. 0.5 mm, included; stigmas 3. Achenes dark brown to black, dull to shiny, 3-4 mm, usually ovoid, sharply trigonous, punctate to smooth, apex acute.
"Slender annual 1–2 m, reclining on other plants, or erect when young, the stems 4-angled, reflexed-prickly as are usually also the petioles and peduncles and the midrib beneath, lvs sometimes pubescent on margins, lanceolate to elliptic, 2–10 cm, to 2.5 cm wide, sagittate at base, the lobes directed downwards; infl of short, head-like, long-peduncled terminal and axillary racemes seldom over 1 cm; perianth pink to white or green; style 1.5 mm, trifid to the middle; achene trigonous, 2.2–3 mm; 2n=40. Marshes and wet meadows; Nf. and Que. to Sask., s. to Ga. and Tex. (Tracaulon s.)"