Plants: What's toxic and what's not
To keep this relatively short I'm only going to focus on common houseplants. There are a lot of trees, bushes, and outdoor plants that have some toxic principle but we could be here all day going through all of those and most pets are not wandering free in gardens munching plants-usually they find something better to check out like mole hills or dead stuff!
The good news is that while many common houseplants can make your pet mildly ill most are not "toxic" in the deadly sense. Some of the plants that fall into this category are the Caladium spp, Colocasia spp, Dieffenbachia spp, Philodendron spp. Some of the common names for these plants include Dumb Cane, Mother in Law's Tongue, and Elephant ear.
The toxic principle for these plants is that calcium oxalate crystals are released upon chewing which causes oral irritation (there may be drooling and swelling of mouth tissues. Larger amounts can cause other GI sign such as vomiting and diarrhea. Treatment is to rinse the mouth with milk or water and use other symptomatic treatment as needed.
The following plants are frequently seen in homes around various holidays, although some may be present year round.
Christmas cactus causes similar signs as Poinsettia and the treatment is the same.
For more information on toxic plants visit the ASPCA Animal Poison Control Center