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Poison Hemlock: Identifying an invasive and toxic plant and toxic look-alikes: Part 1 of 2

This article will focus on identification of the plant and a future article will discuss tips for safe and proper removal of the plant on your property

POISON HEMLOCK (Conium maculatum)

Why should I be concerned about poison hemlock?

Poison hemlock is a toxic and invasive plant that is becoming increasingly more prevalent across the Pennsylvania landscape, especially along roadsides, fields and pastures. All parts of the plant are extremely poisonous to humans and livestock and are often confused with non-toxic members of the parsley family (Apiaceae or Umbelliferae) such as parsley, anise, and chervil. Poisoning typically occurs when people confuse the leaves with parsley, the roots with wild parsnips, and the seeds with anise. Thus, proper identification and avoidance is important.

How can I identify poison hemlock and its look-a-likes?

The first step in identifying, avoiding, and controlling poison hemlock is to learn to identify its different forms and know where to look for it. Introduced from Europe around the 1800s, it has since naturalized across Pennsylvania, and is commonly found in lower elevations along roadside ditches, field edges, and floodplains. As it tends to favor moist areas, stream banks and pastures are common places where clusters of poison hemlock may crop up, as well.

As a biennial plant that takes two years to develop, poison hemlock forms a rosette in the first year, and then grows tall stems with white umbrella-like flowers in the second year. The second-year stems are hollow, stout, and hairless with purple spots. (Pictured above: the stem of a poison hemlock stem, Delaware News,


The Apiaceae or Umbelliferae, also known as the celery, carrot or parsley family, are a family of mostly aromatic plants with hollow stems. While many plants in this family are edible with medicinal properties, others are highly toxic to people and animals and can easily be confused with edible members of the family with potentially disastrous consequences. As most of these plants are non-native and invasive, becoming more prevalent across the landscape and often found growing together, chances of exposure to these highly dangerous plants increases. Given the similar habitats and appearance of these plants, as well as their different chemicals and modes of action, it is important to properly identify them and implement effective management options for control.

All of the plants listed below, except for water hemlock, have a biennial life cycle, meaning they take two years to mature, produce seed, and die. The first year is spent in a vegetative stage as a low-growing rosette. It is in this stage where control is most effective, yet also when they are easiest to confuse and harder to spot. Plants “bolt” in year two, producing multi-branched stems with umbrella-like flowers. Below is a useful comparison between these look-a-likes.

1. Poison Hemlock (Conium maculatum)

Poison hemlock is one of the deadliest plants found in North America. It is perhaps most famous for being used to kill Socrates. Non-native and invasive, it is becoming increasingly more prevalent, especially along roadsides and fields. All parts of the plant contain piperidine alkaloids, especially the flowers and unripe fruits, are extremely poisonous to humans and livestock and are often confused with non-toxic members of the parsley family (Apiaceae or Umbelliferae) such as parsley, anise, and chervil. Unlike some other members of this family, the toxins are not as likely to cause skin rashes or blistering. Poisoning typically occurs through ingestion when people confuse the leaves with parsley, the roots with wild parsnips, and the seeds with anise. Sap on the skin can also introduce toxins through the eyes or from improper handling of food, as can accidental inhalation through nasal passages if burning the plants.

2. Wild Parsnip (Pastinaca sativa)

Yellow flowers help distinguish this species from the others in this list but contact with the plant produces similar reactions of photosensitivity. Tolerant of a wide range of environmental conditions, wild parsnip often invades disturbed areas and is commonly found with poison hemlock.

3. Cow Parsnip (Heracleum maximum

This native, biennial to short-lived perennial plant contains furanocoumarins that produce phytophotodermatitis in the form of a blistering, itchy rash when sap on the skin is exposed to sunlight. Like poison hemlock and wild parsnip, it grows best in moist soils and is common along roadside ditches and pastures.

4. Wild Chervil (Anthriscus sylvestris)

Wild chervil cap can cause a chemical burn on the skin when exposed to sunlight, much like that of wild parsnip. Introduced to North America in wild seed mixes, it can tolerate a wide range of conditions and can spread aggressively, choking out crops and desirable native species. Once established, it is difficult to control.

5. Giant Hogweed (Heracleum mantegazzianum)

Encounters with this giant-sized plant (nicknamed “Queen Anne’s Lace on steroids”) can produce dangerous side effects to many unfortunate individuals who stumble upon it. Its sap contains toxic chemicals called furanocoumarins that cause severe burns and blistering when exposed to the sun’s ultraviolet light and may even cause blindness upon eye contact. This is one plant experts warn you should not attempt to remove on your own. Luckily, its gigantic size (leaves can grow up to five feet wide), makes it fairly easy to spot and avoid. If you do come in contact with it, wash the affected area immediately with soap and water and avoid sunlight for 48 hours.

6. Spotted Water Hemlock (Cicuta maculate)

The perennial water hemlock contains fascicled tuberous roots with multichambered systems that are extremely poisonous if ingested after pulling from the ground. The principal toxins, cicutoxin and oenanthotoxin, act as GABA antagonists in the central nervous system, leading to seizures and in some cases death. This water-loving plant is primarily found along streams and ponds and not likely to be found along roadsides and upland meadows.

7. Queen Anne’s Lace (Daucus carota)

While not nearly as dangerous as its counterparts, wild carrot can produce skin irritations for those with sensitive skin and can easily be confused with more dangerous plants, such as poison hemlock.

Useful websites:

Don’t touch these plants! | U.S. Fish & Wildlife Service (

Wild chervil identification and control: Anthriscus sylvestris - King County

Wild Parsnip | Cornell Weed Identification Poison hemlock identification and control - Agriculture ( Poison Hemlock Identification and Management | University of Maryland Extension (

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