Sium suave

Water Parsnip

Sium suave, Water Parsnip, courtesy Brousseau Collection
Water Parsnip
Photo courtesy Brousseau Collection

Flora, fauna, earth, and sky...
The natural history of the northwoods


  • Sium, from the Latin, sion, "water parsley"
  • suave, from the Latin, suâvis, "sweet"
  • Water Parsnip, from its perceived similarity to the parsnip and its wetland habitat.
  • Other common names include: Hemlock Water Parsnip


  • Kingdom Plantae, the Plants
    • Division Magnoliophyta, the Angiosperms (flowering plants)
      • Class Magnoliopsida, the Dicotyledons
      • Subclass Rosidae
        • Order Apiales
          • Family Apiaceae (Umbelliferaceae), the Parsley and Carrots, 2850 species in 275 genera of global distribution but mostly north temperate regions. Includes the common herbs anise, carrot, celery, coriander, dill, fennel, parsley, and parsnip, as well as the highly toxic hemlocks.
            • Genus Sium, the Water Parsnips
  • Taxonomic Serial Number: 29558
  • Also known as Sium cicutifolium, Sium floridanum, Sium suave var. floridanum
  • Family Apiaceae characterised by alternate leaves, widening at the base into a sheath that clasps the stem. Stems often furrowed. Flowers usually compound, almost always concentrated in flat-topped umbels. Flowers have 5 petals, usually uneven, and 5 stamens. Seeds and fruit form below where the petals and stamen originate. Fruit two-chambered, separating into two, single-seed fruits at maturity. Some part of the plant usually has a strong aroma, due primarily to various oils produced by the plant.


  • A hardy lakeshore perennial of shallow water, 3'-6½' tall.
  • Leaves alternate, oblong to ovate in outline, divided into 11-15 leaflets. Leaves under water divided into thread-like or linear segments.
  • Leaflets lanceolate, pointed tip, tapering to base, sharply toothed, up to 5" long and 2" across. Petioles long below, shorter upward, hollow.
  • Stem erect, branched, angular, smooth; strongly ribbed upward, thickened, and hollow with cross-partitions at the base, partitioned at the nodes above.
  • Flower white or greenish-white, up to 2/3" across, in a compound umbel.
    • Petals 5, white, free from each other, up to 1/3" long.
    • Sepals 5, green; minute or absent.
    • Stamens 5.
    • Pistils
    • Ovary inferior, smooth.
  • Fruit oval, with several prominent and corky vertical ribs, 1/6" long. Ripens July - September.
  • Roots fibrous


  • An emergent wetland plant
  • Identifiable as one of the Apiaceae by its broad, flat flower clusters, hollow stem, and clasping leaves.
  • Distinguished from similar members of the Carrot/Parsley family by its once-pinnate leaves with toothed leaflets. Very similar to poisonous Spotted Water Hemlock (Cicuta maculata) but lacks the purplish mottling on the stem, the multiple leaftlet divisions, and the leaflet veins ending in notches, which characterise its toxic cousin.
  • Because it is often difficult to clearly distinguish similar members of the Carrot/Parsley family from one another, and because some are highly toxic, it is always best to excercise caution and due prudence in dealing with these plants.


  • Newfoundland to British Columbia, south to Florida, Texas, and California


  • Edges of ponds and lakes; shallow waters, often emergent
  • Also wet woods and thickets, swamps, muddy banks, meadows, and roadside ditches.




  • Stems and leaves are toxic and will kill livestock


  • Reproduces by seed and vegetatively by rhizomes
  • Flowering: July-September.


  • By seed and division.
  • Sow late winter/early spring in a cold frame. Slow to germinate.
  • Divide in early spring just before new growth begins.


  • Hardy to USDA Zone 3 (average minimum annual temperature -40ºF)
    • Cultural Requirements
    • Full Sun/Partial Shade
    • Light, rich, moisture retentive soil.
    • Wet soil
  • Very showy in bloom.
  • Available by mail and online from specialty suppliers



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Last updated on 26 February, 2004