by Joelle Steele

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You probably have at least one poisonous plant growing in your garden, and probably several in your neighborhood. The substances found in these plants can be deadly. The following is a list of a few of the most common poisonous plant species, along with their plant family name, common names, and symptoms of poisoning.

Abrus precatorius [Fabaceae] (precatory bean, rosary pea). A single seed can kill an adult. Symptoms may not appear for one to three days. Phytotoxins are abrin and the tetanic glycoside, abric acid, which are chemically related to the toxins produced by bacteria and snake venoms. Symptoms of poisoning include anemia, circulatory collapse, cold sweat, coma, convulsions, diarrhea, drowsiness, fast pulse, general weakness, kidney failure, labored breathing, nausea, severe stomach pain, trembling, vomiting, and weak pulse. May cause death. The seeds are large and used as beads on Mexican necklaces. The plant is grown in the south and central parts of Florida

Aconitum napellus, A. columbianum [Ranunculaceae] (monkshood, wolfsbane, aconite, buttercup). Grows in cool, damp, mountainous areas. Has blue or yellow flowers. A. ferox roots are the source of the Nepalese poison "bikh" (a.k.a. "bish" or "nabee"). Aconitum's toxic properties come from pseudaconitine, one of the deadliest poisons. It causes a tingling sensation in the mouth, skin, and stomach, followed by vomiting, diarrhea, muscular weakness, spasms, weak pulse, respiratory failure, dimming vision, low blood pressure, and convulsions. There is no antidote. Even a small drop of the plant can be fatal. The roots and sees are most toxic, containing aconine and aconitine, and are at their most toxic when the plant is in its pre-flowering stage. The roots can be mistaken for horseradish.

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Amanita phalloides, A. muscaria [Amanitaceae] (destroying angel, deadly amanita, death cap, fly agaric). This is the most dangerous species of mushroom in North America. It accounts for 90% of all mushroom poisonings in the United States. Only one or two mushrooms can kill, even after being cooked. As little as one-third of a mushroom cap can kill a child. Symptoms occur from six to 24 hours after ingestion: intense abdominal pain, profuse vomiting, diarrhea, circulatory failure, coma, liver damage (resulting in jaundice), Usually fatal; recovery is rare even after treatment.

Astragalus spp. [Leguminosae] (locoweed). Contains alkaloids that are toxic. There are hundreds of species, all toxic, even when they are dried out. All are capable of causing immediate death or chronic poisoning which ultimately leads to death.

Atropa belladonna [Solanaceae] (deadly nightshade). This plant is an ornamental in the southwest part of the United States. The bulbs contain the toxic alkaloids, which cause respiratory paralysis. A mere three berries can kill a child.

Buxus longifolia [Buxaceae] (box tree). This plant's black glossy seeds can be fatal when eaten, particularly by children.

Caladium spp. [Araceae] (elephant ears). The parts of these plants all contain calcium oxalate raphides which cause burning and intense irritation of the lips, mouth, and pharynx.

Cicuta maculata, C. douglasii, Cicuta spp. [Apiaceae, Umbelliferae] (water hemlock, cowbane). This is probably the most violently poisonous plant in the northern temperate zone of the world. At least 30% of all poisonings are fatal. The roots and new growth are the most toxic, as is the fruit. The toxins act on the central nervous system causing frothing at the mouth, spasms, tremors, dilated pupils, intestinal distress and pain, diarrhea, convulsions, delirium, respiratory failure, paralysis, and death. A single mouthful or two bites of the root is enough to kill an adult male within 30 minutes or less.

Claviceps purpurea [Clavicipitaceae] (ergot). This is a fungal disease of grain, which when ingested causes seizures and hallucinations.

Codiaeum tiglium, Codiaeum spp. [Euphorbiaceae] (croton). Ingestion of the seeds, which contain "oil of croton," cause a burning pain in the mouth and stomach, rapid heartbeat, bloody diarrhea, coma, and in severe cases, death. A lot of seeds have to be ingested by an adult to be fatal.

Colchicum autumnale [Colchicaceae] (autumn crocus). The toxin in this plant is an alkaloid called colchicine, which is present in all parts of the plant. When ingested, symptoms of poisoning include a burning in the mouth, nausea, vomiting, severe diarrhea, respiratory problems, muscle weakness, kidney failure, circulatory collapse, shock, and often death.

Conium maculatum [Apiaceae, Umbelliferae] (poison hemlock). The leaves of this plant are often mistaken for parsley. The seeds and the roots are the most toxic, as they contain the alkaloid conine and other related alkaloids. The plant has a very unpleasant taste, so voluntary ingestion is unlikely.

Convallaria majalis [Convallariceae, Liliaceae, Ruscaceae] (lily of the valley). This plant contains a glycoside, convallatoxin, which is similar to the action of digitalis. It acts as a stimulus to the heart and also contains irritating saponins. The water in which lily of the valley is kept is poisonous and can kill if accidentally ingested. Symptoms of poisoning include mouth pain, nausea, vomiting, abdominal pain, cramping, diarrhea, headache, dizziness, hallucinations, depression, heart failure, and death.

Cyanophyta [Nostocaceae, Oscillatoriaceae] (blue green algae). The entire plant is toxic, and if either drinking or swimming in water with dense blooms, symptoms of poisoning can occur within 15-45 minutes, death in 1-24 hours. Symptoms include nausea, vomiting, abdominal pain, diarrhea, muscle tremors, difficulty breathing, bluish skin, convulsing, general paralysis, and death.

Datura meteloides [Solanaceae] (jimson weed, devil's weed, moonflower). The seeds are toxic, and only 20 can cause poisoning in an adult. Symptoms of poisoning include dry mouth, thirst, redness of skin, disturbed vision, pupil dilation, nausea, vomiting, headache, hallucinations, excitement, rapid pulse, delirium, incoherent speech, convulsions, elevated temperature, high blood pressure, coma and, in severe cases, death.

Dieffenbachia maculata [Araceae] (dumb cane). The leaves contain water-insoluble calcium oxalate raphides and protein-based toxins. There is immediate and intense pain on contact with the mouth. The mucus lining swells and speech may become intelligible or impossible. Contact dermatitis and inflammation of the cornea and the conjunctiva are also common.

Epipremnum aureum [Araceae] (golden pothos, devil's ivy). The leaves contain calcium oxalate raphides. These cause burning and swelling of the tissues in the mouth. Skin contact may result in dermatitis. With ingestion there may be diarrhea.

Euphorbia spp. [Euphorbiaceae] (euphorbia). There are over 1,500 species. Most of them produce a milky latex that contains complex terpenes (unsaturated hydrocarbons). Contact with the latex causes dermatitis, inflammation of the conjunctiva and cornea, and gastritis. Poinsettias do not contain the toxic terpenes common to other species.

Galanthus nivalis [Amaryllidaceae] (snowdrop). The bulb contains lycorine which affects the heart and nervous system. Symptoms of poisoning include nausea, vomiting, and diarrhea.

Gelsemium sempervirens [Loganiaceae, Gelsemiaceae] (yellow jasmine). The roots and nectar contain the alkaloids gelsemine and gelseminine. Symptoms of poisoning include profuse sweating, nausea, vomiting, muscle weakness, double vision, convulsions, respiratory problems, paralysis of motor nerves, and death.

Gloriosa spp. [Colchicaceae, Ruscaceae] (gloriosa lily). The tubers are the most toxic and contain colchicine and other poisonous alkaloids which result in death within four hours of ingestion. Contact with the mouth results in numbness and burning of the lips, tongue, and throat. Ingestion results in burning of the stomach, vomiting, diarrhea, difficulty breathing, shock, convulsions, respiratory failure, and death.

Hedera helix, H. canariensis [Araliaceae] (English ivy, Algerian ivy). The leaves and berries are poisonous, containing hederin. Symptoms of poisoning include burning in the throat, gastroenteritis, vomiting, and diarrhea.

Helleborus niger [Ranunculaceae] (Christmas rose). The entire plant contains digitalis-like glycosides, saponins, and irritants called protoanemonins. Symptoms of poisoning include pain in the mouth and abdomen, nausea, vomiting, cramping, and diarrhea. Toxicity of the digitalis glycoside can result in rhythmic disturbances in the heart.

Hippeastrum spp. [Amaryllidaceae] (amaryllis). The bulb contains emetic lycorine and small amounts of related alkaloids. Ingestion in large amounts results in nausea, vomiting, and diarrhea.

Hydrangea spp. [Hydrangeaceae] (hydrangea). The flower buds are extremely toxic containing a glycoside which reacts with water or saliva to release cyanide ions. The symptoms of poisoning include abdominal pain, vomiting, lethargy, sweating, and sometimes coma.

Hyoscyamus niger [Solanaceae] (henbane). This is an herb that produces a fetid odor when crushed. The seed pods or seeds themselves contain the alkaloid hyoscyamine, which can be fatal when ingested by a child.

Iris spp. [Iridaceae] (iris). The roots of some species are toxic. They contain an irritant resin. Symptoms of poisoning include stomach and intestinal pain, nausea, vomiting, and diarrhea.

Lantana spp. [Verbenaceae] (lantana). This plant is found all over the United States. It's green berries are the most toxic part. Symptoms of poisoning include stomach and intestinal irritation, bloody diarrhea, vomiting, muscular weakness, jaundice, circulatory collapse and, in severe cases, death.

Lobelia cardinalis, Lobelia spp. [Campanulaceae, Lobeliaceae] (lobelia). All parts of the plant are poisonous and contain lobeline, lobelamine, and other alkaloids. Can be fatal. Symptoms of poisoning include nausea, vomiting, dizziness, headache, sweating, exhaustion, weakness, lowered temperature, prostration, feeble pulse, dilated pupils, abdominal pain, stupor, tremors, convulsions, respiratory failure, and coma.

Malus sylvestris [Rosaceae] (apple). The seeds contain prussic acid (cyanide). A single cup of seeds is sufficient to be fatal. Symptoms of poisoning include nausea, vomiting, abdominal pain, diarrhea, muscle tremors, difficulty breathing, bluish skin, convulsing, general paralysis and, in severe cases, death.

Manihot spp. [Euphorbiaceae] (cassavas, tapiocas, maniocs). The roots are toxic when raw. They contain amygdalin, a soluble cyanogenetic glycoside that breaks down into hydrocyanic acid (cyanide). Symptoms of poisoning include muscular incoordination, convulsions, coma, and death, usually within minutes of ingestion.

Monstera deliciosa [Araceae] (split-leaf philodendron, Swiss cheese plant). Contact between the leaves and the mouth results in burning of the lips and mouth, acute inflammation, blistering and swelling of the tissues, hoarseness, and difficulty swallowing.

Narcissus spp. [Amaryllidaceae] (daffodil, jonquil, narcissus). The bulbs contain lycorine, which can paralyze the heart and number the central nervous system. The bulbs also contain alkaloids. Symptoms of poisoning include nausea, vomiting, and diarrhea.

Nerium oleander [Apocynaceae] (oleander). Ingestion of a single leaf can be fatal to an adult, usually within the space of one day. The plant contains the cardiac glycosides oleandrin and nerioside (which produces physiological effects similar to those of digitalis). Symptoms of poisoning include nausea, vomiting, stomach pain, bloody diarrhea, dizziness, slowed pulse rate, cold extremities, irregular heartbeat, dilated pupils, drowsiness, unconsciousness, lung paralysis, convulsions, coma, and death.

Papaver somniferum [Papaveraceae] (common poppy). It is not legal to cultivate the opium poppy, so it should not be confused with a garden poppy. The poison is in the morphine and other plant alkaloids found in the dried milky sap and fruits (not the seeds like those used on top of breads). Symptoms of poisoning include shallow and slow breathing, stupor, respiratory distress, circulatory depression, coma, and death.

Philodendron scandens [Araceae] (heartleaf philodendron). The leaves contain raphides (needle-like, water insoluble crystals which cause painful itching), which contain calcium oxalate (a salt or ester of poisonous oxalic acid) in addition to irritant proteins. Symptoms of poisoning on contact with the mouth include pain and burning of the lips, mouth, and tongue, and on ingestion, pain and burning of the throat. Contact with the plant juices can result in dermatitis.

Phoradendron species [Viscaceae, Santalaceae] (mistletoe). The berries are the most toxic. They contain the amines beta-phenylethylamine and tyramine which can be fatal within a few hours. Symptoms of poisoning include stomach and intestinal pain, diarrhea, nausea, vomiting, difficulty breathing, delirium, convulsions, slow pulse, collapse, heart failure, and death.

Prunus caroliniana [Rosaceae] (laurel cherry, Carolina cherry). This is an ornamental plant found in the southwest of the United States. The seeds and leaves contain the cyanogenic glycoside amygdalin, which breaks down into the toxic hydrocyanic (prussic) acid (cyanide) when hydrolyzed. The seeds are the most toxic. Symptoms of poisoning include dizziness, spasms, stupor, twitching, paralysis of the l cords, convulsions, coma, and sometimes death.

Ricinus communis [Euphorbiaceae] (castor bean). The entire plant is toxic owing to the phytotoxin ricin. The seeds are especially toxic. Ingesting only 2-8 can be fatal to an adult in one to twelve days. Symptoms of poisoning include burning of the mouth, nausea, vomiting, stomach pain, bloody diarrhea, excessive thirst, prostration, dullness of vision, convulsions, kidney failure, circulatory collapse, and death.

Solanum nigrum [Solanaceae] (black nightshade). The unripe berries contain glyco-alkaloid solanine. Even a small amount can be fatal. Symptoms of poisoning include headache, stomach pain, vomiting, diarrhea, dilated pupils, below normal body temperature, shock, circulatory and respiratory depression, loss of sensation, paralysis, and death.

Solanum tuberosum [Solanaceae] (potato). The tubers themselves contain solanine, which affects the nervous system. It is most concentrated in the layer next to the skin, particularly in green skin areas, and also in the "eye" or sprouts. Ingestion of solanine can be fatal.

Sophora secundiflora, Sophora spp. [Fabaceae] (mescal bean). The seeds are most toxic and contain cytisine and other poisonous alkaloids. The seeds have to be crushed or chewed to be poisonous. A single seed chewed by a child can be fatal. Symptoms of poisoning include nausea, vomiting, diarrhea, excitement, delirium, hallucinations, coma, and death.

Spathiphyllum spp. [Araceae] (peace lily, white anthurium). All parts of the plant contain water insoluble raphides of calcium oxalate. Contact with the mouth results in burning, irritation, and swelling of the lips, mouth, tongue, and pharynx. Ingestion causes gastroenteritis. Root juices can cause contact dermatitis.

Strychnos nux vomica, Strychnos spp. [Loganiaceae] (poison nut). This tree from India is the primary commercial source of strychnine, which is found mainly in the bark and seeds. It has a very bitter taste due to the monoacid base causing an alkaline reaction. It rapidly enters the bloodstream where it then acts on the central nervous system. Symptoms of poisoning occur within 15-20 minutes and include stiffness at the back of the neck, muscle twitching, a feeling of impending suffocation, whole body convulsions alternating with relaxation periods, and death.

Thevetia peruviana [Apocynaceae] (yellow oleander). The fruit is the most toxic. It contains the toxic cardiac glycosides thevetin and peruvoside, and it has effects similar to those of digitalis. A single fruit can be fatal to an adult. Symptoms of poisoning include nausea, vomiting, diarrhea, dilated pupils, drowsiness, irregular pulse and heartbeat, high blood pressure, convulsions, heart failure, and death.

Zantedeschia spp. [Araceae] (calla lily). The leaves contain raphides of calcium oxalate. When ingested, these cause burning in the mouth and lips, sometimes with inflammation and swelling.

Zigadenus paniculatus [Liliaceae] (deathcamas). The bulbs contain the toxins and can be fatal. They are often mistaken for wild onion or garlic.

This article last updated: 09/11/2010.