Water-parsley

Sium suave, commonly known as hemlock waterparsnip or water-parsley, is a perennial herb in the family Apiaceae native to wetlands across much of North America and northern and eastern Asia, where it grows in marshes, swamps, slow streams, ditches and pond margins. It grows from a cluster of fleshy fascicled roots, producing erect stout, hollow, ridged stems 0.5 to 2 metres tall. The leaves are pinnately compound with 7 to 17 narrowly lanceolate, sharply and finely serrate leaflets 3 to 10 centimetres long; submerged or basal leaves are often more finely divided into thread-like segments. In mid to late summer the stems bear flat-topped compound umbels 5 to 12 centimetres across of small white five-petaled flowers, subtended by conspicuous narrow bracts and bracteoles. The fruit is a small ovoid ribbed schizocarp. The species is superficially similar to and often confused with the highly poisonous water hemlock (Cicuta spp.), so all wild Apiaceae from wetlands require careful identification.