Conium maculatum
Poison hemlock
Photo by Chez Brungraber
Family: Apiaceae · Type: Herb · Not Native
Conservation status: Cal-IPC Yes
Conium maculatum (Poison hemlock) is a non-native California herb in the Apiaceae family, recognized by Only Conium species worldwide, representing a monotypic genus in the carrot family.
Poison hemlock is a naturalized biennial found in California Floristic Province and Great Basin regions in moist, disturbed places at elevations below 1,500 meters. Flowering from April to July, this plant produces small white flowers in delicate, many-branched clusters with 10 to 20 rays. Growing 50 to 300 centimeters tall with distinctively purple-spotted or purple-streaked stems, it develops a widely branching structure. Its complex leaves are two-pinnate, with broad triangular blades up to 30 centimeters long and dilated leaf stalks. The small oval fruits are approximately 2 to 3 millimeters wide with generally wavy ribs.
Identification and appearance
Key characters: Only Conium species worldwide, representing a monotypic genus in the carrot family
Habitat and range
Habitat: Common. Moist, especially disturbed places
Elevation: < 1500 m
California counties: Los Angeles, Tulare, Mendocino, Butte, San Luis Obispo, Orange, Santa Cruz, Kern, San Bernardino, Monterey, Alameda, San Diego, San Mateo, Sonoma, San Joaquin, Santa Barbara, Riverside, San Francisco, Tuolumne, Humboldt, Ventura, Marin, Mono, Modoc, Santa Clara, Contra Costa, Merced, Siskiyou, Placer, Sacramento, Sutter, Amador, Yolo, Solano, Glenn, Tehama, Lassen, Napa, Del Norte, Nevada, Trinity, Sierra, Colusa, Stanislaus, El Dorado
Outside California: America, native to Europe
Bloom period
Conium maculatum blooms Apr-Jul.
Conservation status
Cal-IPC Yes
How to tell it apart
vs Anthriscus: Conium has purple-spotted smooth stems; Anthriscus has unspotted hairy stems and beaked fruits.; vs Torilis: Conium has smooth fruits with wavy ribs; Torilis has fruits covered with hooked bristles.; vs Foeniculum: Foeniculum has thread-like leaves and anise scent; Conium has broader leaflets and musty odor.; vs Daucus: Conium has purple-spotted stems; Daucus has hairy stems and fruits that curl into a bird's-nest.; vs Heracleum: Heracleum is massive with huge leaves and unspotted stems; Conium has purple-spotted stems.
Frequently asked questions
Is Conium maculatum native to California?
No. Conium maculatum is not native to California (recorded as not native).
When does Conium maculatum bloom?
Conium maculatum blooms Apr-Jul.
Where in California does Conium maculatum grow?
Conium maculatum occurs in Los Angeles, Tulare, Mendocino, Butte, San Luis Obispo, Orange, Santa Cruz, Kern and other counties, at elevations of < 1500 m.
What plant family does Conium maculatum belong to?
Conium maculatum is in the Apiaceae family, genus Conium.
Is Conium maculatum invasive in California?
Conium maculatum is listed by Cal-IPC with an invasiveness rating of Yes.
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.