Plants which are Toxic and Poisonous to Humans

Many plants can cause dermatitis through contact, poisoning through ingestion, or allergic reactions through either route. People’s susceptibility varies greatly, but many plants are especially dangerous, including some grown as ornamentals in and around homes.

Toxicity of ornamental plants is not a major issue in general, but it is worth mentioning because children and pets are especially vulnerable, and fatalities are possible. The majority of accidental human poisoning by plant ingestion occurs in children under the age of five, but even in this age group, poisoning from plants is uncommon compared to poisoning from common household substances (such as drugs and cleaning supplies).

The majority of the time, we focus on plants to provide colour where it looks best – indoors or in the landscape. When we buy, plant, or grow a plant, we rarely consider the plant’s potential health hazards; instead, we consider beauty, colour, form, and function.

A recurring concern is ornamental plants with berries purchased for Christmas. The colourful fruits of some ornamental peppers are appealing to small children (and pets), and have resulted in numerous calls to poison control centres; in large doses, they can cause irritation (severe in some individuals), as well as vomiting and diarrhoea, but the effects are usually transient. Similarly, the bright red berries of holly are appealing to children and pets, and unless large quantities are consumed, vomiting and diarrhoea are usually the only side effects. The white berries of mistletoe (most commonly (Raf.) Reveal & M.C. Johnst., commonly called) in North American households during the holiday season are also of limited danger unless consumed in large quantities.

Toxic Plants – Alphabetically

• Amaryllis ( ; not , which is also toxic), bulb: gastric irritation.
• Angel’s trumpet ( , ), all parts: delirium, convulsions.
• Autumn Crocus & Star of Bethlehem – Again the bulbs are considered the toxic part which can cause nervous excitement and vomiting when ingested.
• Azalea ( ) all parts: nausea, vomiting, depression, difficult breathing, prostration, coma; potentially fatal.
• Bleeding heart ( (Andrews) Walp.), foliage, roots: may be poisonous in large amounts.
• Caladium, elephant’s ear ( (Ait.) Vent.), all parts: gastric irritation; potentially fatal. (“Elephant’s ear” refers to several unrelated plants, one of which is a food plant.)
• Castor bean ( L.), seeds: one or two seeds can kill an adult.
• Chinese evergreen ( ), entire plant: mouth, throat, & gastric irritation.
• Croton ( (L.) A. Juss.), entire plant, especially sap: dermatitis, gastric irritation.
• Cyclamen ( Mill.), corm: gastric irritation.
• Daffodil ( ), bulbs: nausea, vomiting, diarrhea; potentially fatal.
• Daphne ( L.), berries: several fruits can kill a small child.
• Delphinium, larkspur ( ), all parts: digestive upset, nervousness, depression; potentially fatal.
• Dieffenbachia, dumb cane ( ), all parts: burning, irritation of mouth & tongue; asphyxiation is possible if base of tongue swells & blocks throat.
• English ivy ( L.), all parts: mouth, throat, & gastric irritation.
• Foxglove ( L.), leaves: dangerously irregular heartbeat and pulse, digestive upset, mental confusion; potentially fatal.
• Hyacinth ( L.), The flowers and bulbs are the toxic part and have been know to cause nausea, vomiting and diarrhea, which can be fatal.
• Iris ( ), bulbs: severe digestive upset.
• Jack-in-the-Pulpit – All parts of the plant but especially roots are toxic. Very much like the “Dumb Cane Plant” (Dieffenbachia) which causes burning and irritation of the mouth and tongue from the small calcium oxalate needle-like crystals contained in the plant.
• Jasmine ( ), berries: digestive disturbance, nervous symptoms; potentially fatal.
• Lily-of-the-valley ( L.), leaves, flowers: irregular heart beat and pulse, digestive upset, mental confusion.
• Oleander ( L.), leaves, branches: affects heart; severe indigestion; potentially fatal.
• Philodendron ( ), entire plant: mouth & throat irritation, dermatitis.
• Poke Milkweed
• Poinsettia ( Willd. ex Klotzsch), sap, leaves, stems: mild dermatitis in some people, slight potential for gastric irritation, but only if large amounts are consumed; reports of toxicity have been greatly exaggerated.
• Poison Oak – The acorns and foliage are known to be toxic especially when eaten. The symptoms slowly appear over days or weeks and can gradually affect the kidneys. However, it takes a large quantity amount for poisoning.
• Pothos, devil’s ivy ( (Linden & André) G.S. Bunting), entire plant: mouth, throat, & gastric irritation & swelling, dermatitis.
• Rosary Pea, Castor Bean – The seeds of rosary pea and castor bean or castor oil plants are what to watch out for on these plants. The results can be fatal. It’s been noted that one single Rosary Pea seed has caused death. For adults just one or two Castor Bean seeds are close to a lethal dose.
• Sweet pea ( L.), seeds, seedlings, and pods: slow pulse, respiratory distress, convulsions.
• Tulip ( ), bulbs: abdominal pain, sweating, nausea, vomiting, skin irritation; considered to have limited toxicity, but potentially fatal if large amounts are ingested.
• Wisteria ( ), all parts, especially seeds, pods: vomiting, diarrhea, gastric irritation.
• Yew ( ), seeds, foliage: potentially fatal (reddish flesh of berries has been consumed, but seeds are very toxic).
  

Remember that some people will react to plants while others will not. Furthermore, humans differ from cats and dogs. Animals have different levels of tolerance for and against plants. Always treat unknown plants with respect, and make it a point to teach your children to do the same. Which poisonous plants do you grow?

Sources: Canadian Botanical Association