by Joelle Steele

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All plants are composed of various chemical substances, but some are toxic only to humans, some only to animals, and others are poisonous to both. The poisonous aspect of a plant is primarily due to the presence of one of the following organic compounds: alkaloids, glycosides, organic acids, resins, and phytotoxins. In addition, there are other substances that can cause a plant to be poisonous, such as nitrates and selenium.


Alkaloids have a nitrogen-containing organic base. Alkaloids are colorless, odorless, nearly insoluble in water, and very bitter in taste. Alkali-like poisons — of which more than 5,000 types have been found in plants — all contain nitrogen which forms salts with acids. Sources of all alkaloids are flowering plants. Notable alkaloids are:

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Opiates and Codeines of the opium poppy

Atropine-Nicotine groups in the Solanaceae (nightshade family)

Curines (curare poisons) in tropical members of several plant families

Alkaloids generally produce physiological reactions in the nervous system. These reactions may be violent and acute or may be chronic.


Glycosides (which are part glucoside) are complex carbohydrates which, on hydrolysis and in the presence of amino acids or enzymes, produce one or more simple sugars and non-sugar end products called aglycon. These carbohydrates are water soluble, bitter, often odor-producing and may be colored or colorless. Three primary groups of plant glycosides yielding toxic products on hydrolysis are:

Cyanogenetic glycosides in which the poisonous by-product is hydrocyanic acid or prussic acid such as that found in the species of Sorghum, Prunus (wild cherries, almonds) and Linum (flax), and which leaves an odor of almonds on the breath and body tissues after death (from benzaldehyde)

Saponin glycosides which can dissolve red blood cells and which are produced in the species of Agrostemma (cockle), Digitalis (foxglove), and Actinea (rubberweed)

Solanine glycosides produced in members of the nightshade family, especially berries of Solanum. Cardiac glycosides are sugar compounds that act on the heart

These sugars are chemically bonded to another molecule. There are approximately 400 different ones in plants. Among the common names for glycosides are digitoxin and oleandrin. The hydrocyanic acids cause death by asphyxiation within minutes to an hour, by blocking the oxygen from the red blood cells to the tissues.


Only a few organic acids commonly found in plants are toxic in the amount or in the form in which they occur naturally. The family of nettles (Urticaceae) gets its irritating properties from formic acid in the hairs of the leaves and stems of most species. The toxic properties of Prunus species (leaves, bark, and seeds) depend on the generation of hydrocyanic acid. Oxalic acid — the most common organic acid poison — usually occurs in the form of oxalates, which are present in considerable amounts in the leaves of rhubarb, in Oxalis and Rumex species, and in the rhizomes of the Jack-in-the-pulpit. Oxalic acid poisoning results in colic, depression, coma, kidney failure, and death. Other organic acids include amino acid compounds such as those found in the amanita mushroom.


Resins are the toxic resins or resinoids which occur in poisonous members of the heath family (Ericaceae), water hemlock (Cicuta) of the carrot family, and in the milkweeds (Asclepiadaceae). For the most part, these resins are an insoluble gummy material of complex organic structure, localized in the resin- or latex-containing ducts of the plant. Their poisonous effects occur in the nerves and muscles.


Phytotoxins are the toxic proteins in plants which become non-toxic when they are heated. They are readily absorbed without being broken down in the digestive system, and that is what makes them so very dangerous when they are eaten.


Poisoning from a plant can take the form of:

Blood poisons such as those found in Prunus, or in the seeds of the castor bean (Ricinus) and rosary pea (Abrus)

Nerve poisons such as those found in poisonous mushrooms, Jimson weed (Datura), and henbane (Hyoscyamus)

Neuromuscular poisons such as those found in the ergot fungus, and in foxglove and arrow poisons (curare)

Muscular poisons such as those found in false hellebore (Veratrum)

A poisoning can be either acute or chronic. When there is a single dose of poison immediately followed by symptoms that imperil the victim, the poisoning is considered to be acute. However, when a person has been consuming a poison in low dosages for weeks or months and gradually begins to notice symptoms such as indigestion, a rash, or some form of nerve problems, then the poisoning would be considered to be chronic.

It is difficult to diagnose poisoning from other types of health problems unless there is a history from a patient that indicates what they ate or with what they came in contact. A victim of poisoning can only be treated properly if the exact type of poison is known. Also, the dose of poison needed to kill differs from one person to another depending on the health and condition of the person.

In some cases, vomiting can be induced with water or milk to remove the poisons from the system. In more severe cases, the stomach may need to be pumped, particularly if the poisoning victim is unconscious. However, induced vomiting should not be used as a routine procedure, since it can cause additional corrosive damage to the mouth and throat, as well as the rest of the upper gastrointestinal system, and it could also force the toxic substances into the bronchi and lungs. If the victim is not breathing (the most common result of acute poisoning), or if they are in shock or having convulsions, they should be immediately transported to an emergency room. While most plant poisonings do not kill immediately, some, such as the cyanides, can kill within a few minutes. So, if in doubt, head for the nearest ER.

This article last updated: 09/10/2010.