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Federal Noxious Weed
TDA Noxious Weed
TPWD Prohibited Exotic Species
Invasive Plant Atlas of the US

NOTE: means species is on that list.

Conium maculatum


Poison hemlock

Synonym(s):
Family: Apiaceae (Carrot Family)
Duration and Habit: Biennial Herb

Additional Images

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Photographer: Eric Coombs
Source: Oregon Department of Agriculture, Bugwood.org

Description

Erect, biennial, up to 8' tall forb; stems green with purple spots, freely branched, and hollow; all parts deadly poisonous.
Flower gives an 'umbrella appearance' with white, 5-parted; inflorescence of many 2"-3 1/2" mostly terminal umbels often with 2-4 together from the top stem node. Over time, the side umbels overtop the central one. Blooms are from June to August.

Native Lookalikes: Currently no information available here yet, or there are no native Texas species that could be confused with Poison hemlock.

Ecological Threat: All plant parts are poisonous; however, the seeds contain the highest concentration of poison. (It was probably used to poison Socrates.) It contains highly poisonous alkaloids toxic to all classes of livestock and humans. Human deaths have occurred from harvesting and consuming the roots as wild carrots or parsnips. It may act as a pioneer species quickly colonizing disturbed sites and displacing natives during early successional areas.

Biology & Spread: Poison hemlock is an herbaceous (soft stem) plant that reproduces solely by seeds. The seeds separate from the plant when it becomes mature, and despite the plantís prolific seed production, does not have a mechanism for long-distance seed dispersal. The seeds drop close to the parent plant and may be spread over distance by water, birds, and rodents and remain viable for only two to three years.

History: Poison hemlock is native to Europe and was introduced into North America in the 1800s as an ornamental.

U.S. Habitat: Waste places, weedy areas, and woodland borders.

Distribution

U.S. Nativity: Introduced to U.S.

Native Origin: Europe

U.S. Present: AL, AR, AZ, CA, CO, CT, DE, GA, IA, ID, IL, IN, KS, KY, LA, MA, MD, ME, MI, MN, MO, MT, NC, ND, NE, NH, NJ, NM, NV, NY, OH, OK, OR, PA, RI, SC, SD, TN, TX, UT, VA, VT, WA, WI, WV, WY

Distribution in Texas: Reported along the I-10 cooridor in central and west Texas. Also from Dallas and Houston areas.
Recent citizen reports confirm it is still present in North Texas.

Mapping

Invaders of Texas Map: Conium maculatum
EDDMapS: Conium maculatum
USDA Plants Texas County Map: Conium maculatum

Invaders of Texas Observations

List All Observations of Conium maculatum reported by Citizen Scientists

Native Alternatives

There are many species that can resemble Poison Hemlock because of the 'white umbrella of flowers'.
This PDF here can show the difference between this invasive and native such as Ragweed, Elderberry, Yarrow and Angelica.

  • It also shows similarities between Poison Hemlock and Giant Hogweed, Wild Carrot and Wild Parsnip.

Management

Due to the noxious nature of the plant, it is highly recommended that you call a professional to handle this plant. You may need to combine mechanical and chemical control for best results, and it may take more than one or two years to control this weed.

Mechanical: If you choose to manage poison hemlock yourself, be sure to wear gloves and other protective clothing including eye wear. Shower afterwards to be sure you have no toxic sap on your skin, and launder your clothes.

Mechanical: There are several herbicides (e.g. glyphosate, or 2,4-D) on the market to control poison hemlock. Most of these herbicides require you to apply it to this weed early in the season when this plant is in a seeding or small rosette stage. This may require you to carefully spot spray the rosette. If it is too late for your chemical control measures for this year, start planning your control measures for next year/next season today!

USE PESTICIDES WISELY: ALWAYS READ THE ENTIRE PESTICIDE LABEL CAREFULLY, FOLLOW ALL MIXING AND APPLICATION INSTRUCTIONS AND WEAR ALL RECOMMENDED PERSONAL PROTECTIVE GEAR AND CLOTHING. CONTACT YOUR STATE DEPARTMENT OF AGRICULTURE FOR ANY ADDITIONAL PESTICIDE USE REQUIREMENTS, RESTRICTIONS OR RECOMMENDATIONS. MENTION OF PESTICIDE PRODUCTS ON THIS WEB SITE DOES NOT CONSTITUTE ENDORSEMENT OF ANY MATERIAL.

Text References

(Bailey, L.H. and E.Z. Bailey. 1977. Hortus Third: A Concise Dictionary of Plants Cultivated in the United States and Canada, MacMillan Publishing Co., Inc., New York.

USDA, NRCS. 2001. The PLANTS Database, Version 3.1, National Plant Data Center, Baton Rouge, LA 70874-4490 USA. - http://plants.usda.gov/

USDA Forest Service, Forest Health Staff, Newtown Square, PA. Invasive Plants website: http://www.na.fs.fed.us/fhp/invasive_plants.

Online Resources

https://extension.umn.edu/identify-invasive-species/poison-hemlock

https://extension.umd.edu/resource/poison-hemlock-identification-and-management/

Search Online

Google Search: Conium maculatum
Google Images: Conium maculatum
NatureServe Explorer: Conium maculatum
USDA Plants: Conium maculatum
Invasive Plant Atlas of the United States: Conium maculatum
Bugwood Network Images: Conium maculatum

Last Updated: 2024-02-08 by Ashley Morgan-Olvera, TISI
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