Poison Hemlock vs Queen Anne's Lace: The Stem Test

Safety first. Poison hemlock is highly toxic. Do not touch it, taste it or crush it to identify it. All parts of the plant contain coniine, and the roots and seeds carry the highest concentration. If you think someone has eaten any part of it, call Poison Control at 1-800-222-1222 or go to an emergency department now. If the person has collapsed, has a seizure, has trouble breathing or cannot be woken, call 911.

If sap gets on your skin, wash it off and keep that skin out of the sun. The sap is also a skin irritant.

The stem test

Do not start with the flower. Start with the stem, at eye level, on a plant you have not touched.

• Poison hemlock: smooth, hairless, hollow, and marked with purple or red blotches. On a mature plant it is 1 to 2 inches across.
• Queen Anne’s lace: covered in stiff, bristly hairs. It is much thinner.
• Wild parsnip: also has a hairless, grooved stem, but its flowers are yellow. It can cause burns too. Do not touch it.
• Cow parsnip: much larger leaves, with white flowers and fine hairs. It can also cause burns. For that pair, see cow parsnip vs giant hogweed.

If the stem is smooth and has purple blotches, stop. Do not part the foliage with your hands to get a better look.

The flower is a second check

Queen Anne’s lace has a flat-topped cluster 2 to 4 inches wide, usually with a single deep purple floret in the center. Poison hemlock’s white flowers are held in flat-topped clusters 4 to 6 inches across. Wild parsnip’s flowers are yellow.

Field guides also mention bracts under the flower head. Treat bracts as a third check for someone with the plant in hand, not as the test you bet your skin on. The stem is the character that matters at arm’s length.

Why one look is not enough

Poison Control warns that at some stages of growth, the purple spots or the bad smell may not be present. The smell is described as musty or like mouse urine, but you should never crush the plant to check. A plant with no spots and no smell can still be hemlock.

That is why the rule is simple: if you are not certain, treat it as poison hemlock. Certainty means the stem, the leaf and the flower all agree, not one of the three.

What hemlock does to people

Early symptoms include nausea and vomiting, excessive salivation, sweating and muscle weakness. As the poison affects the nervous system, it can cause tremors, seizures, paralysis and breathing difficulty. Muscle damage and kidney failure can occur in severe cases. Symptoms can progress quickly, and Poison Control says it is not safe to treat an exposure at home.

Poison hemlock is also toxic to livestock. Wisconsin DNR reports that a single plant can produce more than 30,000 seeds, and Poison Control notes that the seeds can stay viable in the soil for 3 to 6 years. A patch that is pulled this year can return from the seedbank for several years.

Removing it safely

Do not pull mature poison hemlock with bare hands. Penn State Extension notes that the taproot is about 10 inches long, hand removal is difficult, and the sap is a skin irritant. Even a weed trimmer needs precautions so plant material does not contact your body.

Penn State lists diquat, pelargonic acid, glyphosate and 2,4-D as post-emergent active ingredients, and says first-year rosettes are the best target. Wisconsin DNR lists 2,4-D plus dicamba before buds form. These are active ingredients named by the sources, not rates or recommendations for your site. Follow the product label; the label is the law.

For protective equipment, timing and disposal, see poison hemlock removal. For the species profile, see poison hemlock. For the other pairs, see look-alikes.