Fl. Carniol. ed. 2, 2: 251. 1772.
Leaves connate at base, obovate-spatulate to ± round, 4–9 × 1–4 mm, 1+-veined. Stem and leaf scales present. Inflorescences: bracts persistent. Pedicels 0–0.2 mm in fruit. Flowers solitary; styles erect; pollen yellow. Schizocarps 1.2–1.8 × 1–1.7 mm, ± as long as wide; mericarps pale grayish brown, not swollen, winged throughout, wings straight, 0.1–0.5 mm wide. 2n = 10.
Phenology: Flowering May–Oct.
Habitat: Standing water, stream margins, backwaters, ponds, pools, ditches.
Elevation: 0–1500 m.
Introduced; St. Pierre and Miquelon, B.C., Nfld. and Labr. (Nfld.), Que., Ala., Calif., Conn., Maine, Md., Mass., Mo., Mont., N.J., N.Y., Oreg., Pa., Va., Wash., Wis., Europe, introduced also in Australia.