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Missouri Environment & Garden


David Trinklein
University of Missouri
Plant Science & Technology
(573) 882-9631

Beware of Poisonous Plants

David Trinklein
University of Missouri
(573) 882-9631

Published: March 12, 2021


Every year, approximately two million accidental poisonings are reported to poison control centers across the United States. This is equivalent to one every 15 seconds. Unfortunately, nearly three percent of all poisonings are plant-related. The third full week of March each year is designated as National Poison Prevention Week and serves as an opportunity to educate the public about the danger of poisonings and how to prevent them.

Although plants are essential for our well-being, there are a number of plant species that can be harmful. It has been estimated that more than 500 species of plants growing in the United States contain compounds that are toxic to humans. Some poisonous plants have become such an integral part of our lives that many of us have lost track of the fact that they (or certain of their parts) are potentially harmful. For example, the tubers of Irish potato (Solanum tuberosum) are an important energy source for many people. Yet, if ingested, it leaves and other green parts can cause significant gastric distress, because of a toxic compound they contain called solanine.

A poisonous plant can be defined as "any plant possessing a property injurious to man or animals." The term "injurious" can imply allergic reactions caused by spores or pollen, skin rashes caused by dermal contact with plants, and internal poisonings caused by ingestion of plant material. Those plants responsible for internal poisonings often are divided into those that cause minor reactions such as vomiting or diarrhea, and those that cause major, more serious, reactions. It is the latter type of poisoning that causes the greatest concern relative to human safety.


Interestingly, many poisonous plants are of significant medicinal value in that the toxic compound, when administered in small, controlled dosages, has valuable therapeutic properties (e.g., digitalis derived from foxglove). It should be obvious, because of the risk involved, that self-medication with plants or substances derived from plants should be avoided.

In other cases, the toxic agents in poisonous plants have been isolated and used as pesticides. For example, when nicotine derived from tobacco is combined with sulfur a very potent insecticide known as nicotine sulfate is formed. Once marketed as Black Leaf 40®, it was banned by the EPA in 2014.

The substances that cause plants to be poisonous are biologically active chemicals that are formed through many different pathways within plants. Most are secondary metabolites (by-products) resulting from essential functions and provide the plant with valuable side-effects because of their toxicity. For example, a toxic metabolite produced by a plant can increase its chances of survival by deterring animals and insects from using it as a food source. These toxic substances are very diverse but can be classified into one of eight different groups, all having one thing in common-they interfere with the metabolism of other living organisms, which makes them poisonous.

Plant-related poisonings are more common among children rather than adults. This partly stems from the fact that children are inquisitive by nature and might be tempted to sample a brightly colored berry or other interesting plant part, when adults would not. Secondly, most poisons are rated in toxicity according to the amount that must be ingested per unit of body weight (i.e., mg active ingredient/kg body weight) to produce toxicity symptoms. Since children weigh less than adults, it takes less of a toxic compound to produce visible symptoms of poisonings in children than in adults. Keeping poisonous plants out of the ready access by children is key to preventing poisoning.

Plant poisoning in adults most often results from consuming unknown or incorrectly identified plant material, rather than from experimentation. Education concerning which plants are poisonous is essential for preventing poisoning. The following are a few fairly common plants that are considered to be highly poisonous:

  • Oleander (Nerium oleander)
  • Water Hemlock (Cicuta sp.)
  • Rosary Pea (Abrus precatorius)
  • Deadly Nightshade (Atropa belladonna)
  • Castor Bean (Ricinus communis)

    Castor Bean

  • English Yew (Taxus baccata)
  • White Snakeroot (Ageratina altissima)

    White Snakeroot

  • Monkshood (Aconitum sp.)


The Missouri Poison Center (800-222-1222) located in St. Louis maintains a 24/7 hotline for questions about possible poisonings by plants or other toxic materials. Additionally, its website contains an extensive list of plants that are toxic, although relatively few pictures are included (https://missouripoisoncenter.org/wp-content/uploads/2015/02/Toxic-and-NonToxic-Plants.pdf).

Illustrated books describing poisonous plants can be very helpful in their identification. Basic Illustrated Poisonous and Psychoactive Plants by Jim Meuninck is an example of one such book. Others books are available as are internet sites that describe poisonous plants. Examples of informative internet sites include Poisonous and Non-poisonous Plants, An Illustrated List, (https://www.poison.org/articles/plant), and List of Poisonous Plants an interactive website maintained by the Canadian government describing plants toxic to humans, dogs and/or cats (https://www.cbif.gc.ca/acp/eng/poisonous-plants/search).

  • It is important to remember that prevention is the best cure for plant-related poisonings. The following are a few common-sense suggestions that will help prevent accidental poisonings:
  • Become familiar with the plants in and around your home (common and scientific names) and know which ones are poisonous. Consult a reliable reference if necessary.
  • Instruct children never to put a plant or plant part in their mouth.
  • Keep all known poisonous plants away from your home or well out of the reach of children.
  • Never store non-food plants in your refrigerator.
  • Never use flowers or other plant parts for food unless you are certain they are non-toxic and their production history is known. Pesticides used on ornamental plants are not necessarily labeled for food plants.
  • Never experiment when it comes to consuming plants of unknown identity or toxicity.

If you suspect someone has consumed a poisonous plant, immediate action should be taken. Do not wait for symptoms to appear. While it is important to act quickly, it is equally important not to panic. Remove any plant parts from the person's mouth and give the person a small amount of water or milk to drink. Next, call 911, the nationwide Poison Information Center (1-800-222-1222) or your local hospital. Try to identify the plant that was eaten and, if possible, collect a small sample of the plant. Give the plant sample to the professionals who administer medical treatment to the victim.

Poisonous plants have been a part of our daily lives for millennia. Their presence is not a cause for alarm as long as we know the dangers involved and are aware of the risk implied by their presence. Education is key for preventing accidents from happening.

Disclaimer: The preceding article was written for educational purposes only. Please contact a physician or the nationwide poison information center (800-222-1222) if you suspect someone has ingested a poisonous plant.

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REVISED: March 13, 2021