![]() ![]() It is the plant used to kill Socrates as well as the Greek statemen Theramenes and Phocion. This non-native is one of the deadliest plants found in North America. Since that time, poison hemlock has elevated its profile from an uncommon oddity to a common threat. Rogue plants remained relatively rare until around 30 years ago. as an ornamental in the late 1800s from Europe, West Asia, and North Africa. Poison hemlock was imported into the U.S. Both are prolific seed producers with seeds remaining viable for 4 – 6 years for poison hemlock and around 4 years for wild parsnip. Mature wild parsnip plants are shorter in stature but still impressive at up to 4 – 5 ft. Mature poison hemlock plants can measure 6 – 10 ft. However, it may occasionally behave as a monocarpic perennial spending more than a year in the vegetative stage before flowering once and then dying. Wild parsnip is also reported to have a biennial life cycle. Plants “bolt” during the second year “reproductive stage” to produce erect multi-branched stems topped with umbrella-like flowers. Poison hemlock has a biennial life cycle. The first year is spent in the “vegetative stage” as a low-growing basal rosette the stage that is currently very apparent. They superficially share floral characteristics with other members of the carrot family such as Queen Anne’s lace ( Daucus carota) however, this non-native biennial blooms much later in the season. Poison hemlock and wild parsnip belong to the so-called carrot family, Apiaceae (= Umbelliferae). This is important to understand relative to management options as well as medical treatments for exposure to these highly dangerous weeds. However, the defense chemicals of these weeds are very different and have vastly different modes of action. The stems do not have purple blotches.Poison hemlock ( Conium maculatum L.) and wild parsnip ( Pastinaca sativa L.) are combined in this report because these invasive non-native weeds are increasingly found growing together in Ohio. Wild parsnip can be distinguished by its celery-like leaves and yellow flowers. The similarities with poison hemlock end here. Wild parsnip ( Pastinaca sativa) is a tall plant that you should never touch because it’s so toxic.Also, Queen Anne’s lace has lacy bracts under the white flower heads. The plant is also toxic. The stem of Queen Anne’s lace, however, is hairy and it does not have purple blotches. Queen Anne’s Lace ( Daucus carota) is often confused with poison hemlock because of its lacy leaves.The stems may have purple spots like poison hemlock but the leaves look different, they are deeply incised and not lacy. Giant hogweed ( Heracleum mantegazzianum) grows much taller than poison hemlock, up to 15 to 20 feet in height, and it is just as invasive and toxic.The location can also give you cues, as water hemlock grows primarily in wet locations such as ditches, stream banks, pond margins, and marshes. The stems of water hemlock are pale green with purple stripes, which distinguishes them from the spotted or blotchy stems of the poison hemlock. ![]() While it might take a trained eye to distinguish the flowers–umbels of small white flowers on tall stems that can reach up to 6 feet in height-from those of poison hemlock the stems are different. Spotted water hemlock ( Cicuta maculata) and western water hemlock ( Cicuta douglasii) are two related native species that are both highly toxic, just as poison hemlock.The stem is green without any purple spots and the deeply lobed leaves are much larger than poison hemlock. Its flower head is distinctly different, much larger and up to 1 foot across. Cow parsnip ( Heracleum lanatum) is as tall as poison hemlock and also toxic.Tall meadow rue ( Thalictrum dasycarpum) can have purple spots on green stems.Common yarrow ( Achillea millefolium) leaves are feathery and fern-like and the plant is much smaller, about 3 feet.The inconspicuous green flowers in the late summer are located at the end of the branches. Common ragweed ( Ambrosia artemisiifolia) has very lacy leaves, but the stems are hairy.Elderberry has oblong, sharply serrated leaves and woody stems without any purple spots. American elderberry ( Sambucus canadensis) also has white flowers that are much larger than those of poison hemlock.The leaves are compound and sharply toothed, not lacy. Angelica ( Angelica atropurpurea) shares purple stems with poison hemlock.The Spruce Home Improvement Review Board. ![]()
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