23 Poisonous Plants to Avoid & Their Health Impacts

Nature’s bounty includes plants that, while often beautiful, harbor dangerous toxins. These plants can cause a range of health issues, from mild irritations to fatal outcomes.

Whether you’re a gardener, hiker, or simply a nature enthusiast, knowledge of these toxic plants is essential for protecting yourself and your loved ones.

1. Oleander (Nerium oleander)

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Oleander is an ornamental shrub with pink, red, or white flowers commonly found in warm climates. Every part of the plant is toxic, containing cardiac glycosides like oleandrin that can disrupt the heart’s electrical activity.

Ingestion can lead to symptoms such as nausea, vomiting, diarrhea, erratic heart rate, and potentially fatal cardiac arrest ¹.

The plant’s widespread use in landscaping makes accidental exposures not uncommon, emphasizing the need for caution.

2. Rhododendron (Rhododendron spp.)

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Rhododendrons, including azaleas, contain grayanotoxins that can alter sodium channels in the body, affecting the nervous system and muscles.

Symptoms of poisoning include drooling, vomiting, diarrhea, low blood pressure, and, in severe cases, coma or death ².

The toxin’s ability to disrupt cellular function underscores the plant’s danger, especially to children and pets attracted by its vibrant blooms.

3. Deadly Nightshade (Atropa belladonna)

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Deadly nightshade is a herbaceous perennial with purple bell-shaped flowers and shiny black berries.

It contains atropine and scopolamine, which block neurotransmitters in the nervous system, leading to symptoms such as blurred vision, hallucinations, rapid pulse, and, in severe cases, respiratory failure and death ³.

The plant’s historical use in poisons and cosmetics highlights its potent toxicity.

4. Castor Bean (Ricinus communis)

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The castor bean plant is the source of castor oil, yet its seeds contain the deadly poison ricin ⁴. Ricin inhibits protein synthesis, causing cell death. Symptoms of poisoning include nausea, vomiting, abdominal pain, and, within severe cases, seizures, organ failure, and death.

A single seed can be fatal to a child, illustrating the extreme danger posed by this plant.

5. Foxglove (Digitalis purpurea)

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Foxglove plants are sources of digoxin and digitoxin, which are used medically to treat heart conditions ⁵. However, accidental ingestion can lead to an overdose, causing nausea, vomiting, visual disturbances, and life-threatening cardiac irregularities.

The fine line between medicine and poison with foxglove underscores the importance of proper identification and use.

6. Water Hemlock (Cicuta spp.)

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Water hemlock is considered one of the most poisonous plants in North America. It contains cicutoxin, a potent neurotoxin that causes seizures and abdominal cramps and can lead to death within a few hours of ingestion (within 60 minutes ⁶).

The toxin directly impacts the central nervous system, making this plant extremely dangerous.

7. Dumb Cane (Dieffenbachia)

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Dumb cane is a popular houseplant with a toxic sap that contains calcium oxalate crystals. When chewed, it can cause intense oral irritation, difficulty swallowing, and temporary speechlessness.

The immediate and painful symptoms serve as a rapid warning of the plant’s toxicity.

8. Monkshood (Aconitum napellus)

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Monkshood, also known as wolfsbane, contains aconitine, a potent neurotoxin that disrupts sodium channels in the heart and nervous system ⁷.

Ingestion or skin contact can lead to gastrointestinal discomfort, heart palpitations, and paralysis, which can be fatal. Its stunning appearance belies its deadly nature, requiring cautious handling.

9. Lantana (Lantana camera)

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Lantana’s bright flowers and berries contain triterpenoid compounds that are toxic to humans and animals, causing liver damage and other symptoms like weakness, vomiting, and diarrhea.

Its attractive appearance to children and pets adds to its risk as an ornamental plant in gardens (it’s a favorite of mine since Lantana blooms all summer).

10. Autumn Crocus (Colchicum autumnale)

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The autumn crocus resembles harmless spring flowers but contains colchicine, a powerful compound used to treat gout. However, it is toxic in uncontrolled doses.

Symptoms of colchicine poisoning include severe gastrointestinal distress, kidney failure, and multi-organ damage, potentially leading to death ⁸. This plant’s beauty masks its danger, particularly during its blooming season.

11. Jimson Weed (Datura stramonium)

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Jimson weed contains tropane alkaloids, which cause delirium, hallucinations, and an elevated heart rate. These symptoms can escalate to fatal respiratory and cardiac arrest.

The plant’s widespread occurrence, especially in rural areas ⁹, and its hallucinogenic properties often lead to accidental poisonings.

12. Yew (Taxus spp.)

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Yew trees, commonly used in landscaping, contain taxine, a compound that disrupts the heart’s electrical activity, leading to sudden cardiac arrest ¹⁰. Interestingly, the tree’s red berries are not toxic, but the seeds inside them are, as are all other parts of the plant.

The yew’s association with both life and death throughout history reflects its dual nature as a decorative yet deadly plant.

13. Angel’s Trumpet (Brugmansia spp.)

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Angel’s trumpet, with its large, pendulous flowers, contains scopolamine and atropine, leading to symptoms like hallucinations, muscle weakness, and, if ingested in sufficient quantities, death.

The plant’s striking appearance and intoxicating scent make it a popular ornamental yet dangerously toxic.

14. Sago Palm (Cycas revoluta)

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Despite its name, the sago palm is not a true palm but a cycad. It contains cycasin, a toxin that can cause liver failure, seizures, and death in humans and pets.

Its popularity in landscaping and as a houseplant necessitates awareness of its toxic potential.

15. White Snakeroot (Ageratina altissima)

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White snakeroot contains tremetol, which can cause milk sickness, a condition historically significant in the Midwest. Symptoms include nausea, abdominal discomfort, and severe fluid electrolyte imbalances, which can lead to death if untreated.

This plant’s ability to poison indirectly through dairy products ¹¹ makes it uniquely hazardous.

16. Hydrangea (Hydrangea spp.)

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Hydrangeas are well-loved for their lush, colorful flower heads. They contain cyanogenic glycosides, which can release cyanide when the plant material is chewed, preventing oxygen molecules from being released effectively from red blood cells.

Symptoms of hydrangea poisoning can include dizziness, confusion, fainting, and, in severe cases, convulsions and death.

The presence of these compounds necessitates caution, especially in areas where children or pets may be tempted to nibble on the attractive flowers.

17. Amaryllis (Amaryllis spp.)

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The amaryllis is a popular bulb plant, especially around the holidays, for its striking flowers. It contains lycorine and other alkaloids that can cause vomiting, diarrhea, abdominal pain, and sometimes hypotension if ingested.

The bulb is the most toxic part. While amaryllis is a festive decoration, its toxic potential should not be underestimated, particularly in households with pets or small children.

18. Manchineel Tree (Hippomane mancinella)

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Dubbed the most dangerous tree in the world (often found in South Florida ¹²), the manchineel tree’s fruit resembles a small apple but is incredibly toxic.

If inhaled, its sap can cause blistering on the skin and burning of the eyes and airway. Ingesting its fruit can lead to severe gastrointestinal and respiratory distress and potentially death.

The tree is found in tropical climates, and caution signs are often posted to warn of its dangers.

19. Mountain Laurel (Kalmia latifolia)

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Mountain laurel, with its attractive pink and white flowers, contains grayanotoxins that disrupt cellular function and can cause nausea, vomiting, drooling, and, in severe cases, low blood pressure and death.

The entire plant is toxic, posing a significant risk to humans and animals, especially in areas where it grows wild.

20. European Bittersweet (Solanum dulcamara)

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This vine, also known as woody nightshade, has attractive purple flowers and red berries that contain solanine, a toxin that affects the nervous system.

Symptoms can include gastrointestinal distress, paralysis, and respiratory failure.

Its berries are particularly appealing to children, making it a hidden danger in gardens and wild areas.

21. Pokeberry (Phytolacca Americana)

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Pokeberry plants are known for their distinctive purple-black berries and are highly toxic to humans and animals. The plant contains saponins and anthraquinones, leading to nausea, vomiting, diarrhea, and severe stomach cramps if ingested.

Despite its toxicity, pokeberry has been used historically in folk medicine and as a dye, highlighting the need for careful handling and identification.

Personal Story: When I first moved into my home I was doing some landscaping. I took out the weed eater and whacked one of these plants. Tried to pull up the broken stem and being unsuccessful went about finishing the rest of the yard.

Due to it being a hot summer day, I then took a break and went inside to get some water. After taking a drink, I realized had a rash all down my forearms. Some quick Google searches, and that’s when I realized you should never touch pokeberry plants with your bare hands!

I knew you should never consume an unidentified plant, but unless it was something like poison ivy, I didn”t realize just touching it could be dangerous (I’ve learned a lot about plants since then :).

22. Caladium (Caladium spp.)

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Caladiums are popular for their striking, heart-shaped leaves, which contain calcium oxalate crystals. If chewed or ingested, these crystals can cause immediate pain and irritation to the mouth, throat, and gastrointestinal tract, leading to difficulty swallowing, drooling, and vomiting.

The plant’s visual appeal often places it within easy reach of children and pets, making education about its toxicity vital for preventing accidental ingestions.

23. Rosary Pea (Abrus precatorius)

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The rosary pea is a plant with seeds that are highly toxic due to the presence of abrin, a protein that inhibits protein synthesis within cells, leading to cell death.

Ingesting even a single seed can be fatal, with symptoms including nausea, vomiting, abdominal pain, and organ failure ¹³.

The seeds are often used in jewelry and rosaries, which poses a risk if they are broken open and the seed is ingested. The rosary pea’s danger, coupled with its use in crafts, necessitates a high degree of caution.

Knowledge & Education

pesticide for houseplants
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Understanding the risks associated with these plants and educating others about their dangers can prevent accidental poisonings and ensure a safe environment for all.

If you love gardening, hiking, or just spending time in nature, it’s crucial to learn about these poisonous plants to keep you and your loved ones safe.

Sources

  1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6996654/
  2. https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/azalea
  3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3361210/
  4. https://emergency.cdc.gov/agent/ricin/facts.asp
  5. https://www.buffalo.edu/news/releases/2020/04/013.html
  6. https://www.fs.usda.gov/wildflowers/plant-of-the-week/cicuta_maculata.shtml
  7. https://www.poison.org/articles/why-is-monkshood-considered-a-poison–174
  8. https://pubmed.ncbi.nlm.nih.gov/15088997/
  9. https://bmcpublichealth.biomedcentral.com/articles/10.1186/s12889-022-12854-1
  10. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5922745/
  11. https://pubmed.ncbi.nlm.nih.gov/2092409/
  12. https://www.nbcmiami.com/news/local/manchineel-tree-found-in-florida-named-deadliest-in-the-world/2623010/
  13. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5416790/
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Davin is a jack-of-all-trades but has professional training and experience in various home and garden subjects. He leans on other experts when needed and edits and fact-checks all articles.