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  • Different portions of the plant (root, stem, leaves, and seeds) often contain different concentrations of a chemical.
  • The age of the plant contributes to variability. Young plants may contain more or less of some constituents than mature plants.
  • Climate and soil influence the synthesis of some chemicals.
  • Plants contain chemicals that may exert toxic effects on skin, lung, cardiovascular system, liver, kidney, bladder, blood, central and peripheral nervous systems, bone, and the reproductive system.
  • Contact dermatitis and photosensitivity are common skin reactions with many plants.
  • Gastrointestinal effects range from local irritation to emesis and/or diarrhea.
  • Cardiac glycosides in the leaves or seeds of many plants cause nausea, vomiting, and cardiac arrhythmias in animals and humans.

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Of the many species of plants that contain toxic chemicals, only a few are described here. Selection has been based on three considerations: frequency with which contact occurs, importance and seriousness of toxic effect, and scientific understanding of the nature of the action of the chemical.

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Toxic effects of the same species of plant may vary with differences in production of the toxic chemical by plants. The reasons for variability in concentration of toxic chemicals are several:

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  1. Different portions of the plant (root, stem, leaves, and seeds) often contain different concentrations of a chemical.

  2. The age of the plant contributes to variability. Young plants may contain more or less of some constituents than mature plants.

  3. Climate and soil influence the synthesis of some chemicals.

  4. Genetic differences within a species may alter the ability of individual plants to synthesize a chemical. Synthesis of related toxic chemicals often is found in taxonomically related species as a characteristic of a genus and sometimes as a familial characteristic.

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Skin

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Contact Dermatitis

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Many plants common to temperate regions worldwide contain compounds that produce irritation on contact with the intact plant. Several species of Ranunculus (buttercup) cause contact dermatitis. These plants contain ranunculin, which releases toxic protoanemonin, also present in Anemone, another genus of the buttercup family. Protoanemonin is readily converted to anemonin, which has marked irritant properties. Ingestion of plants containing protoanemonin may result in severe irritation of the gastrointestinal tract.

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Contact of the eye or tongue to the juice of the Dieffenbachia plant results in pain and rapid development of edema and inflammation, which may take days or weeks to subside. The toxicity is due to: (1) release of a histamine- or serotonin-like chemical that may be involved in the immediate pain and (2) release of raphides, the needle-like crystals of irritating calcium oxalate that are coated with a trypsin-like inflammatory protein, from ampule-shaped ejector cells throughout the surface of the leaf.

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Contact with the trichomes of species of Urtica (nettles) causes pain and erythema after penetration of the skin. In the stinging nettles, Urtica urens and Urtica dioica (family Urticaceae), the trichomes covering the leaves and ...

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