Sium suave
Hemlock water parsnip
(c) naturalist charlie, some rights reserved (CC BY) · licence
Family: Apiaceae · Type: Herb · Native
Sium suave (Hemlock water parsnip) is a native California herb in the Apiaceae family, recognized by Northern range limit species with transcontinental distribution, distinguished from other Apiaceae by specific aquatic habitat requirements.
Hemlock water parsnip is a California native perennial found in central Sierra Nevada, central Great Basin, deltaic Great Valley, and central California Ranges in swamps, marshes, and streambanks at elevations below 2,350 meters. Flowering from July to August, this plant produces small white flowers in delicate compound umbels with 10 to 20 slender rays. Growing with robust stems 60 to 120 centimeters tall, it has thick, segmented stems that rise from wet ground. Its large compound leaves feature multiple linear to lanceolate leaflets, 1 to 4 centimeters long, with serrated edges and irregularly cut margins. The fruit is small, approximately 2 to 3 millimeters wide, typical of plants in the parsnip family.
Identification and appearance
Key characters: Northern range limit species with transcontinental distribution, distinguished from other Apiaceae by specific aquatic habitat requirements
Habitat and range
Habitat: Swamps, marshes, streambanks
Elevation: < 2350 m
California counties: Tulare, Lassen, Modoc, Inyo, Solano, Plumas, Mono, Mendocino, Sacramento, Trinity, San Joaquin, Madera, Napa, Shasta, Mariposa, Siskiyou, Contra Costa, Santa Barbara
Outside California: to British Columbia, eastern North America, eastern Asia
Bloom period
Sium suave blooms Jul-Aug.
How to tell it apart
vs Oenanthe: Sium fruits have thick corky ribs but no crown; Oenanthe fruits have a crown of teeth on top.; vs Berula: Sium has thick, obvious ribs on fruits; Berula has thread-like ribs hidden in the corky wall.; vs Apium: Sium fruit halves stick firmly to the central axis; Apium fruit halves separate cleanly.; vs Perideridia: Sium grows from fibrous roots in wetlands; Perideridia grows from tubers in dry grasslands.; vs Oxypolis: Sium fruits are ribbed but rounded; Oxypolis fruits are flattened front-to-back with thin wings.
Frequently asked questions
Is Sium suave native to California?
Yes. Sium suave is native to California (recorded as native).
When does Sium suave bloom?
Sium suave blooms Jul-Aug.
Where in California does Sium suave grow?
Sium suave occurs in Tulare, Lassen, Modoc, Inyo, Solano, Plumas, Mono, Mendocino and other counties, at elevations of < 2350 m.
What plant family does Sium suave belong to?
Sium suave is in the Apiaceae family, genus Sium.
What habitat does Sium suave grow in?
Sium suave grows in Swamps, marshes, streambanks.
Related species
Other California species in the same genus, family, or bioregion.
Sources: Jepson eFlora · Index of California Plant Names · CalPhotos
Last updated 2026-10-07
Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, Cal-IPC, and more.