Oenanthe aquatica (L.) Poir.

Oenanthe aquatica (L.) Lam. Encyc. 4: 530. 1797
Phellandrium aquaticum L. Sp. PI. 255. 1753.
Lignsticum Phcllandrium Crantz, Stirp. Atistr. 3: 84. 1767.
Oenanthe Phellandrium Lam. Fl. Fr. 3: 432. 1778.
Selinum Phellandrium E. H. L. Krause in Sturm, Fl. Deuts. ed. 2. 12: 93. 1904.
Plants stout, decumbent, or floating and ascending, 5-15 dm. high; leaves ovate in general outline, pinnately decompound, the leaflets ovate, 4-6 mm. long, pinnatifid into linear or oblong ultimate divisions 0.5-3 mm. long, or the ultimate divisions of submerged leaves filiform and elongate; peduncles 1-4 cm. long; involucre wanting, or of a few small bracts; involucel of numerous linear-lanceolate bractlets, 2-3 mm. long, shorter than the pedicels; rays 6-15, unequal, 1-2.5 cm. long; pedicels 3-5 mm. long; calyx-teeth lanceolate, unequal, up to 1 mm. long; styles about 1 mm. long; fruit oblong-oval, 3.5-5 mm. long, 1.5-2 mm. broad, narrowed at the apex, the ribs low and broad, broader than the intervals and the lateral broader than the dorsal. Type locality: "In Europae fossis," collector unknown.
Distribution: Eurasia; introduced at Washington, D. C.