Some of the most popular houseplants are surprisingly toxic. They were chosen not for their suitability as a snack for pets and small children, but for their ability to thrive in a year-round climate of 50 to 70 degrees Fahrenheit. That's why many houseplants are actually tropical plants that come from the jungles of South America and Africa.
The poinsettia, one of the most reviled indoor plants, is not nearly as toxic as its reputation would lead one to believe. As a member of the Euphorbiaceae family, the sap is mildly irritating, but that is the extent of it. While the poinsettia gets plenty of bad press around the holidays, many other houseplants escape notice in spite of their more toxic qualities.
Peace lily, Spathiphyllum spp.
A South American plant with simple white flowers that resemble calla lilies. In 2005 more people called poison control centers about possible peace lily poisoning than any other plant. (This may have more to do with how popular the plant is than how poisonous it is). The plant contains calcium oxalate crystals that can bring on skin irritation, burning of the mouth, difficulty swallowing, and nausea.
English ivy, Hedera helix
This ubiquitous European vine grows outdoors as a ground cover but is also one of the most popular indoor potted plants. The berries are bitter enough to discourage people from eating them, but they could cause severe gastrointestinal problems and possible delirium or respiratory problems. Sap from the leaves can cause serious skin irritation and blisters.
Philodendron, Philodendron spp.
An ivy-like plant native to South America in the West Indies, shown above. All parts of the plant contain calcium oxalates. Nibbling on a leaf might only bring about mild burning in the mouth or a little nausea, but ingesting it could lead to severe abdominal pain, and repeated skin contact my cause serious allergic reactions. Poison control centers in the United States got over sixteen hundred calls in 2006 related to philodendron poisoning.