Conium maculatum

Conium maculatum_poison hemlock_plantb_JM DiTomaso
Photo: Joseph DiTomaso

Common names: poison-hemlock

Conium maculatum (poison-hemlock) is a biennial forb (family Apiaceae). Poison-hemlock has spread throughout California in areas below 5,000 feet (1,500 m) elevation, excluding the Great Basin and Desert provinces and is commonly found in dense patches along roadsides and fields. It also thrives in meadows and pastures and is occasionally found in riparian forests and flood plains, but prefers disturbed areas. All parts of poison-hemlock are toxic to humans and animals when ingested; handling plants can cause contact dermatitis in some people. Poison-hemlock can spread quickly after the rainy season in areas that have been cleared or disturbed. Once established, it is highly competitive and prevents establishment of native plants by over-shading.

Cal-IPC Rating: Moderate?

CDFA Rating: None?


Plant Assessment Form - Information gathered by Cal-IPC on the impacts, rate of spread, and distribution of invasive plants in California. Does not include management information.

Species ID Card

Invasive Species ID Card - To support field identification of early detection species, Cal-IPC has designed a set of Species ID cards that can be downloaded, printed double-sided, and trimmed to size.

Weed Management Notes

  • Management Notes - Information on management techniques and effectiveness from the University of California Cooperative Extension’s Weed Research & Information Center.

Cal-IPC Newsletter Articles

Cal-IPC Symposium Presentations

Presentations are linked where available. Where a presentation is not available, find more information by reading the abstract in the Cal-IPC Symposia Archive.

Other Conium maculatum Information

  • Bugwood - National database from the Center for Invasive Species and Ecosystem Health at the University of Georgia.
  • CalPhotos - Images of plants taken mostly in California.
  • Calflora - Distribution map and records of this species in California.
  • CalWeedMapper - Distribution map of this species in California with ability to determine regional priorities.
  • EDDMapS - Distribution of this species in North America.
  • Jepson Interchange - Information on this plant's taxonomy, biology, and distribution from UC Berkeley's Jepson Herbarium.
  • USDA PLANTS Database - Information on identification and distribution, with links to websites in individual states.
  • Additional photos

    Conium maculatum_poison-hemlock_Jutta Burger_cropped
    Conium maculatum (poison-hemlock) young stem and root. Photo: Jutta Burger
    Conium maculatum_inflorescence_copyright_2009_NealKramer
    Conium maculatum (poison-hemlock) inflorescence. Photo: &#169 2009 Neal Kramer
    Conium maculatum_leaves_copyright_2014_NealKramer
    Conium maculatum (poison-hemlock) leaves. Photo: &#169 2014 Neal Kramer
    Conium maculatum_stem and leaf base_copyright_2009_NealKramer
    Conium maculatum (poison-hemlock) stem and leaf base. Photo: &#169 2009 Neal Kramer
    Conium maculatum_poison hemlock_infestation_JM DiTomaso
    Conium maculatum (poison-hemlock) infestation. Photo: Joseph DiTomaso
    Conium maculatum_poison hemlock_seedling_JM DiTomaso
    Conium maculatum (poison-hemlock) seedling. Photo: Joseph DiTomaso