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Conium maculatum

Scientific Name: Conium maculatum
Common Name: Poison Hemlock

Line Drawing:

Morphological Description:
Grows between 1.5-2.5 meters (3-8 ft) tall
Smooth Green stem
Seeds are the most toxic part of the plant
Hollow stems

Small and white flowers, usually wide with narrow tips
Clustered in umbels up to 10-15 cm across
Umbels are terminal and lateral
Each umbel consists of 10-15 rays and each ray has a secondary umbel with 8-18 flowers
Umbels are about 7.6 cm across
Fruits are ridged and flattened and each holds two seeds
Blossoms in spring and fruits are ripe in Summer
Fruit are 0.08-0.13 inches wide, ovate with ditinctively wavy ribs
Finely divided and lacy, triangular shape
Ranges in size up to 50 centimeters long and 40 cm wide
Yellowish, transparent essential oils of noxious odor from fresh leaf and inflorescence
Shiny green leaves
Fern-like appearance and somewhat filmy upper surface

Habitat & Basic Biology (life history, dispersal abilities):
It was brought to America and Oceania as an ornamental plant
In a normal season, it took 7-8 weeks for these pollinated flowers to develop into fully ripened fruits
Blooming period occurs from late spring to mid summer and lasts about 1-2 months
Produces only by seed which is dispersed by water, mud, wind, animal fur, human clothing, boots, and machinery

Functional traits (photosynthetic rates, phenology, etc.):
Reproduces only from seed
Biennial, winter annual and short-lived perennial plant
Germinate in autumn
Develops throughout winter and spring
Capable of rapid establishment after autumn rains
Prefers sun, light shade, moist conditions and a fertile loamy soil
After blooming, foliage turns yellow and withers away later in the summer.

Distribution (geographic range):

Native to temperate regions: Europe, Western Asia, and North Africa
Introduced to Asia, North and South America, Australia, and New Zealand
It is found on poorly drained soils and along streams, open floodplains, and riparian woodlands
Can also establish stands in dry areas

Evolution (of traits in novel range):
None known.

Performance of invader in CA (interactions with species native to S. CA):
Poison hemlock may act as a pioneer species quickly colonizing disturbed sites and displacing natives during early successional seres. The presence of C. maculatum degrades habitat quality and could indicate a management problem on an ecological preserve

List of references:
Calflora: Information on California plants for education, research and conservation, with data contributed by public and private institutions and individuals, including the Consortium of Calif. Herbaria. [web application]. 2014. Berkeley, California: The Calflora Database [a non-profit organization].Available:   (Accessed: Jun 09, 2014).

Castells, E., Berhow, M.A., Vaughn, S.F., Berenbaum, M.R. (2005). Geographic variation in alkaloid production in Conium maculatum populations experiencing differential herbivory by Agonopterix alstroemeriana. Journal of Chemical Ecology. 31(8):1693-1709.
Berhow demonstrates that hemlock shows excellent potential biological control agent, as it is extremely host-specific on poison hemlock.

Drewitz, Jennifer. “Invasive Plants of California’s Wildland.” Conium Maculatum. Cal-IPC, n.d. Web. 09 June 2014. <>.
The California Invasive Plant Council is a resource that compiles informational factsheets about invasive species.

Gulezian, Paul Z. et al. (2012). Establishment of an Invasive Plant Species (Conium maculatum) in Contaminated Roadside Soil in Cook County, Illinois. The American Midland Naturalist, 168 (2), 375-395.
Gulezian and colleagues analyzed C. maculatum’s tolerance to elevated levels of heavy metal contamination in disturbed soils.

“Noxious Weeds.” Poison-hemlock Identification. King County, 3 Dec. 2013. Web. 09 June 2014. <>.
King County provides comprehensive guides to identifying invasive species such as poison hemlock.

“Plants Profile for Conium Maculatum (poison Hemlock).” Plants Profile for Conium Maculatum (poison Hemlock). USDA, n.d. Web. 09 June 2014. <>.
The USDA provides a comprehensive overview of poison Hemlock along with other invasive species.