(Original Post Date: 6/16/14)
It is important to know if a plant is toxic to pets before it is brought into a household. As there are many different species of plants, exact identification is essential to knowing if it is safe for an animal to chew on. Even if the plant is intended to be higher than an animal can possibly reach, or in a closed room, remember that cats can reach areas that are higher than we may think, leaves or petals can fall off onto the floor, and doors can be accidentally left open. Therefore, it cannot be assumed that a pet will never have any access to plants that are brought into the house. The ASPCA has a useful website that lists both toxic and non-toxic plants: www.aspca.org/pet-care/animal-poison-control/toxic-and-non-toxic-plants.
There is a long list of toxic plants; please note that the following list is only a small subset of some of the more common and/or dangerous ones:
Lilies (species Lilium and Hemerocallis) are very toxic to cats, causing kidney failure. All parts of the plant are toxic, and a cat does not need to ingest much of the plant to take in a toxic dose. A cat can become sick even from drinking the water in the vase that the flowers are sitting in or grooming off some pollen that stuck to their fur.
Signs, such as vomiting, lethargy, lack of appetite, can develop within a few hours after ingestion. Kidney failure can progress within 1-2 days. Aggressive treatment, consisting of intravenous fluids for about 48 hours, digestive protectants, and other supportive care is needed. The sooner treatment is started, the better the prognosis. However, if treatment is started beyond 18-24 hours after a toxic dose is ingested, or if a cat is no longer producing urine, the prognosis for recovery is poor. Rhubarb leaves can also cause kidney failure with similar signs.
Although sago palms are usually found in the tropics, they are often imported to be used as ornamental Bonsai houseplants. Examples of these palms are Cycad, Japanese cycad, Coontie plant, Zamia palm, and Cardbord palm. All parts of these plants are very toxic to dogs, but the seeds are the most toxic parts. The sago palms can cause severe liver damage, leading to liver failure. Symptoms include digestive signs (vomiting, diarrhea, lack of appetite), which occur within a few hours after ingestion, to neurologic signs (tremors, trouble walking, seizures) 2-3 days later. Once signs of liver failure have developed, the prognosis is poor due to permanent liver damage. Amanita mushrooms can also cause liver failure.
Several plants can cause damage to the heart - a few of these include lily of the valley, oleander, rhododendron species, foxglove, azalea, and yews, just to name a few. They will cause abnormal heart rhythms, leading to signs of vomiting, lethargy, leading to weakness and collapse.
Peace lilies, calla lilies (despite their names, neither of these are in the Lilium species), philodendrons, and dumb cane all contain calcium oxalate crystals. They don't normally cause life-threatening signs, but they are locally irritating. They will cause oral pain, salivation, painful swallowing, and lack of appetite. Treatment consists of flushing the mouth, giving milk to bind the crystals, and providing supportive care. Poinsettias contain a sap that is also irritating to the mouth and digestive tract.