There are many plants that are toxic to cats if eaten. The most deadly common houseplants are lilies, but a number of other plants can also have adverse effects. Some toxic plant effects are relatively minor. For example, chrysanthemums and poinsettias can cause skin or mouth rash.
Plants that induce more serious reactions such as pain, vomiting, tremors, and problems with the heart, kidneys, and respiratory system in severe cases include azaleas and umbrella plants. Morning glory, nutmeg, peyote, periwinkle, and marijuana will induce hallucinations in cats. China berry, moonweed, and water hemlock can cause convulsions. Outdoor plants, trees, and shrubs that can have toxic effects include daffodils, delphiniums, marigolds, fox gloves, wisteria (seeds), larkspur, holly, yew, and horse chestnut.
Most outdoor plants will just cause stomach upsets, but there are a few, such as ivy, that can be fatal if larger quantities are ingested. Given the option, most cats are far more inclined to snack on grass than other plants, and they are usually not interested in eating the poisonous ones (though accidental ingestion may occur if there are a lot of poisonous seeds lying around). Growing some cat grass indoors can help prevent munching on houseplants.
Photo by teamK
For a list that provides information on symptoms, see The Cat Owner’s Home Veterinary Handbook: http://www.doctordog.com/catbook/catpoison.html