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Conium maculatum (poison hemlock)

Conium maculatum

Introduced from Europe and western Asia, Conium maculatum can be found throughout the Midwest—though it is more common in a band from Ohio to Missouri. It is, according to legend, the plant used to execute Socrates (who may himself be a legend, but that's a discussion for another day). Conium maculatum is a towering plant, usually appearing along roadsides, in empty lots, next to fields, and in similar waste places. It can be confused with Daucus carota, Queen Anne's lace, since they are both members of the carrot family and have similar features. However, poison hemlock features purplish red spots on its stem (maculatum means "spotted"), while Queen Anne's lace does not. Additionally, poison hemlock appears in late spring and early summer, earlier than Queen Anne's lace, which appears from mid-summer through fall, although there is some overlap. Several other, less common members of the carrot family are also similar, but only Conium maculatum features purple-red spots on its stem. Additional identifying features include the tall size at maturity (up to 8 feet high), the lacy foliage (the leaves are doubly pinnate), and the loosely packed flowerheads containing small, white, 5-petaled flowers. Conium maculatum is poisonous (potentially fatally) to people and to animals when ingested and, according to some sources, it can cause dermatitis when handled.

Range of Conium maculatum

midwestern range


Conium maculatum
maturing plants in midsummer


Conium maculatum
young stem; note glaucous (frosted) surface

 

Conium maculatum
mature stems sometimes develop shallow ridges

 

Conium maculatum
post-mature stems sometimes become purplish red overall

 

Conium maculatum
previous year's stem


Conium maculatum
flowers in loosely clustered flowerheads

 

Conium maculatum
flower buds

Conium maculatum
seed pods


Conium maculatum
lacy, doubly pinnate foliage


Conium maculatum
mature plants in late summer


Conium maculatum
new plants in spring, emerging among canes of previous plants




References: GN Jones 1971, Wilkinson & Jacques 1972, RL Jones 2005, Voss & Reznicek 2012, Kurz 2014, Mohlenbrock 2014, Hilty 2018, USDA 2018.


Kuo, Michael & Melissa Kuo (April, 2018). Conium maculatum (poison hemlock). Retrieved from the midwestnaturalist.com website: www.midwestnaturalist.com/conium_maculatum.html

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