Fool's Watercress

Apium nodiflorum (L.) Lag. Amen. Nat. 101. 1821
S«»»i nodiflorum L. Sp. PI. 251. 1753.
Cicuta nodiflara Crantz, Class. Umbell. 97. 1767.
Seseli nodiflorum Scop. Fl. Cam. ed. 2. 1: 213. 1772.
Sison nodiflorum Brot. Fl. Lusit. 1: 423. 1804.
Pimpinella nodiflora Stokes, Bot. Mat. Med. 2: 149. 1812.
Helosciadium nodiflorum Koch, Nova Acta Acad. Leop.-Carol. 12: 126. 1825.
Helodium nodiflorum Dumort. Fl. Belg. 77. 1827.
Selinum nodiflorum E. H. L. Krause in Sturm, Fl. Deuts. ed. 2. 12: 34. 1904.
Plants aquatic or amphibious, perennial, the stems creeping to ascending or erect, 1.5-10 dm. high or long, from a creeping rhizome and rooting at the lower nodes; leaves oblong in general outline, excluding the petioles up to 3 dm. long, pinnate with 3-9 pairs of leaflets, the leaflets ovate to lanceolate, about 6 cm. long, 1.5 cm. broad, usually crenate-margined, the terminal 3-lobed; umbels sessile or short-pedunculate; involucre of 2 or 3 bracts, or wanting; involucel of 5-8 conspicuous, triangular-lanceolate bractlets, equaling or exceeding the pedicels; rays 15-20, unequal, about 3 cm. long; calyx-teeth obsolete; carpophore entire; fruit broadly oval or oblong-oval, 1-2 mm. long.
Type locality: "In Europa ad ripas tluviorum," collector unknown.
Distribution: Central Europe to northern Africa; introduced on ballast in Pennsylvania, New Jersey, and South Carolina.