Hyacinth, Daffodil

Ingestion of the bulbs can be fatal, causing nausea, vomiting and diarrhea. 

Dieffenbachia, Elephant Ear

All parts of these plants can cause intense burning and irritation of the mouth and tongue.  Death can occur if the base of the tongue swells enough to block the passage of air.

Bleeding Heart

Foliage and roots can be poisonous in large amounts, causing convulsions and other nervous symptoms.  This plant has been fatal to cattle.  

Azalea

All parts are poisonous and cause nausea, vomiting, depression, breathing difficulties, coma. Rarely fatal.

Jimson Weed

All parts of the plant are poisonous, causing abnormal thirst, vision distortions, delirium, incoherence, coma. Often fatal. A significant grazing livestock poison in North America ¹.

Poison Ivy

All parts of this plant contain a highly irritating oil with urushiol.  Skin reactions can include blisters and rashes.  Urishol can be spread readily to clothes and back again, and has a very long life.  Infections can follow scratching.  Despite the common name, urushiol is actually not a poison but an allergen, and because of this it will not affect certain people.  The smoke from burning poison ivy can cause reactions in the lungs and can be fatal ¹.

Autumn Crocus

The bulbs contain colchicine.  Colchicine poisoning has been compared to arsenic poisoning.  Symptoms usually begin 2 to 5 hours after the toxic dose has been ingested, but could be delayed by as much as 24 hours.  Symptoms include burning in the mouth and throat, fever, vomiting, diarrhea, abdominal pain and kidney failure.  Onset of multiple-system organ failure may occur within 24 to 72 hours.  There is no specific antidote for colchicine, although various treatments do exist ¹.

Milkweed

Contains cardenolide toxins, which can stop the heart ¹.

Snow on the Mountain

Luckily, in most species, the sap tastes so bitter that few victims will eat these plants long enough to be seriously affected.  Some people find casual handling causes skin irritation as well.  Ingestion of the leaves causes intense burning of the mouth, throat, and stomach, and uncontrollable salivation. All spurges cause vomiting, nausea, and/or diarrhea if they are eaten.  High doses result in convulsions and sometimes coma and death ².

Castor Bean

Ingesting a SINGLE castor bean can be FATAL.  The seeds contain ricin, and according to the 2007 Guiness Book of World Records, this plant is the most poisonous in the world.  Castor oil, long used as a laxative, is made from the seeds, but the ricin is removed during processing.  If ingested, symptoms typically occur within 2-4 hours.  These include a burning sensation in mouth and throat, abdominal pain, vomiting and bloody diarrhea.  Within several days there is severe dehydration, a drop in blood pressure and a decrease in urine.  Unless treated, death can be expected to occur within 3–5 days; if victims have not succumbed after this time, they often recover ¹.

Larkspur

Young plants and seeds are poisonous, causing nausea, muscle twitches, and paralysis.  Ingestion is often fatal.

Rhubarb leaves

The leaf stalks are edible (rhubarb pie, anyone?), but the leaves contain oxalic acid, which is a nephrotoxin.  Symptoms of poisoning include kidney disorders, convulsions, and coma, though it is rarely fatal ¹.

Glory Lily

Native to southern Africa and Asia, if found in the US this would be a cultivated plant.  All parts of the plant contain colchicine and are dangerously toxic if ingested (see Autumn Crocus above).  Contact with the stems or leaves can cause skin irritation ³.  

Oleander

This is a highly poisonous plant.  It affects the heart and can cause extreme stress to the digestive system.

Foxglove

Ingestion of this plant can be fatal.  The heart drug, Digitalis, is made from foxglove.  Leaves are poisonous in large doses.  Symptoms include elevated heart rate, blood pressure and pulse.  Can cause confusion and disorientation.  

May Apple

Green portions of the plant, unripe fruit, and especially the root contain the toxin podophyllotoxin, which causes diarrhea and severe digestive upset ¹.

Water Hemlock

The root, when freshly pulled out of the ground, is extremely poisonous and contains the toxin cicutoxin.  This is a central nervous system stimulant which can result in seizures ¹.

Jequirity Bean

The glossy red seeds are unfortunately attractive to children.  They are usually about the size of a ladybug with one black dot.  Ingesting a single seed can kill an adult.  Symptoms of poisoning include nausea, vomiting, convulsions, liver failure, and death, usually after several days.  The seeds have been used as beads in jewelry, which is dangerous; inhaled dust is toxic and pinpricks can be fatal ¹.

Rhododendron

All parts of this plant are poisonous and cause nausea, vomiting, depression, breathing difficulties, coma. Rarely fatal.

English Yew

Nearly all parts of this plant contain the toxin taxanes, except the red, fleshy, and slightly sweet berry-like structure surrounding the toxic seeds.  The seeds themselves are particularly toxic if chewed ¹.

Holly

The berries cause gastroenteritis, resulting in nausea, vomiting and diarrhea ¹.

Nightshades

One of the most toxic plants found in the Western Hemisphere.  Ingestion of a single leaf can be fatal to an adult.  The berries pose the greatest threat to children because they look attractive and have a somewhat sweet taste.  The consumption of two to five berries by children and ten to twenty berries by adults can be lethal.  Symptoms of poisoning include dilated pupils, sensitivity to light, blurred vision, tachycardia, loss of balance, staggering, headache, rash, flushing, dry mouth and throat, slurred speech, urinary retention, constipation, confusion, hallucinations, delirium, and convulsions ¹.  

Wisteria

This plant is poisonous to both animals and humans. The seeds and the pods are the most poisonous parts, but all parts of the plant are toxic if consumed.  Symptoms of poisoning are nausea, vomiting, stomach pain and diarrhea ⁴.

Lily of the Valley

Toxins found in this plant (leaves or flowers) cause disorientation and confusion, upset digestive system, irregular heartbeat and pulse.