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NEWS ARCHIVE:     Age: 534 days

Learn to recognize poisonous plants invading the Wisconsin landscape

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Published: June 11, 2013 by the Central Office

MADISON - Two non-native wild plants that are starting to flower in Southern Wisconsin can cause serious harm to people who encounter them, making identification and control of these plants a high priority before they set seed this fall, according to state invasive species specialists.

Poison hemlock and wild parsnip are becoming more common along roadsides and are threatening the integrity of the natural areas as they encroach, says Kelley Kearns, a native plant ecologist with the Department of Natural Resource.

"During their flowering stage is the best time to control these plants, specifically by mowing," Kearns said.

It is said that Greek philosopher Socrates was killed by drinking the juice of poison hemlock. The sap from the plant contains chemical compounds known as neurotoxins that can be absorbed through the skin. The sap of wild parsnip can cause phytophotodermatitis: when skin is exposed to sap in the presence of sunlight, it can cause severe rashes, blisters, and discoloration of the skin.

Both of these plants are members of the carrot family, Apiaceae.

Poison hemlock
Click on image for poison hemlock photo gallery.

"It's hard to believe that such unforgiving plants are relatives to some of our most popular garden plants," Kearns said. "Our edible, garden-grown carrots, parsnips and parsley are all closely to these plants.

Distinguishing these species from their many relatives can be challenging, but Kerns said there area a few defining characteristics that can help aid in identification:

Poison hemlock (Conium maculatum)

  • A defining trait is smooth stems with streaked blotches or purple spots.
  • Tiny five-petaled white flowers bloom in umbels.
  • Leaves are triangular and broad, but finely divided, giving them a lacy appearance.

Wild parsnip (Pastinaca sativa)

  • Small yellow flowers bloom as flat-topped umbels.
  • Wild parsnip
    Click on image for wild parsnip photo gallery

  • Leaves are pinnately compound made up of broad, diamond-shaped leaflets, similar to celery.

Kearns said the best time to control these plants is by mowing them when they are in their flowering stage. The plants should be mowed after flowering heads appear, but before seed is produced. Annual mowing treatments will reduce populations over time.

"Due to their toxic chemical constituents, people need to take precautions when dealing with these plants," Kearns said. "Avoid any direct contact to your skin and minimize inhalation of plant residues. Always wear gloves, long sleeves and pants, as well as safety goggles."

For more help with identification and photographs, search the DNR website for "poison hemlock," or "wild parsnip."

Report occurrences of these species

DNR invasive species specialists are interested in tracking the expanding range of these plants across the state. People who see either of these two species are asked to report them nby sending an email to Include the location and photographs of the population.

FOR MORE INFORMATION CONTACT: Kelly Kearns - 608-267-5066

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Last Revised: Tuesday, June 11, 2013