Poisonous Plants

Disclaimer: The following 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 eaten a poisonous plant.

Plants are critical in helping us sustain our lives. They provide us with food, clothing and shelter in addition to increasing the aesthetic value of our lives through their beauty. For obvious reasons, food plants have been selected for their nutritional value, tastiness and lack of potentially harmful compounds (at least in the part of the plant consumed). Such is not the case with certain non-food plants which, while being a valuable part of our lives, may contain toxins that can be harmful or even fatal to man or animals. It has been estimated that more than 700 species of plants growing in North America have caused illness or death in humans and that more than three percent of all poisonings are plant-related. Some poisonous plants have become such an integral part of our lives that many of us have lost track of the fact they are potentially harmful.

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. It is the latter type of poisoning that causes the greatest concern relative to human safety. Many poisonous plants are of great medicinal value in that the toxic compound, when administered in small, controlled dosages, has valuable healing properties (e.g., digitalis or belladonna). In other cases the toxic agents in poisonous plants have been isolated and used as effective insecticides (e.g., pyrethrum).

The substances that cause plants to be poisonous are biologically active chemicals that are formed through many different pathways within plants. Most are considered to be secondary metabolites (by-products) resulting from essential functions of the plant that provide it with valuable side effects because of their toxicity. For example, a toxic secondary metabolite produced by a plant can increase its chances of survival by deterring animals and insects from using it as a food source. The diversity of toxic compounds in plants is remarkable. Although varied in nature, these toxic compounds 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 toxic. For example, the alkaloids represent a large group of toxic compounds contained by many plants (e.g., members of the Solanaceae [nightshade] family) and are cholinesterase inhibitors that act on the nervous system. Other compounds such as the cardioactive glycosides are steroidal in nature and act as heart stimulants; ingestion of large amounts can lead to heart failure in humans. For a more thorough discussion of the nature of these toxic compounds a comprehensive reference such as A Colour Atlas of Poisonous Plants should be consulted.

Poisoning by ingesting plants is much more common among children 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 to produce an effect (i.e., mg active ingredient/kg body weight). Since children weigh less than adults, it takes less of a toxic compound to produce visible symptoms of poisonings. Keeping poisonous plants out of 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 key to prevent poisoning. The following table is a partial listing of plants that are known to be poisonous. It was provided by the Missouri Poison Center located at Cardinal Glennon Children’s Hospital in St. Louis (800-392-9111).

Always remember that prevention is the best cure for plant poisonings. The following are a few common sense suggestions that will help:

• 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 mouths. Eliminate all known poisonous plants from your home or keep them 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 think someone has eaten a poisonous plant, immediate action should be taken. 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 to drink. Call the nationwide Poison Information Center at (1-800- 222-1222), your local hospital or your local police department (911). Try to identify the plant that was eaten and collect a small sample of the plant if possible. Give the sample to, or identify the plant for, the professionals who administer medical treatment to the victim.

Poisonous plants have been a part of our daily lives for years. 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.

David Trinklein, Department of Horticulture, UMC (573) 882-9631