*Please note that most most animals have good instincts on what not to eat and that large qualities of most houseplants have to be ingested in order for it to have serious effects on an animal's health.
If you find that your pet is prone to crewing on houseplants, consider planting a 'cat grass' planter with oats, barley or even lawn seed, to satisfy their needs in a safe way.
TOXIC
Aloe Vera
Amaryllis: bulbs.
Apple Tree: Stems, leaves, and seeds.
Apricot: Keep dogs, cats, and horses away from apricot stems, leaves, and seeds.
Asparagus fern
Autumn Crocus (Colchicum autumnale)
Azalea
Castor Bean (Ricinus): This plant is highly toxic, but only rarely ingested by pets.
Chrysanthemum (Chrysanthemum)
Cyclamen: roots.
Dieffenbachia
Elephant ear
English Ivy (Hedera helix)
Hyacinths
Jade
Kalanchoe
Lilies (Lilium): leaves, pollen and flowers, especially to cats.
Lily of the Valley
Marijuana (Cannabis)
Oleander (Nerium oleander)
Peace Lily (Spathiphyllum)
Philodendron
Pothos (Epipremnum)
Rhododendron
Sego Palm (Cycas revoluta)
Tulips and Narcissus bulbs (Tulipa and Narcissus)
Yew (Taxus)
NON-TOXIC
African violets,
Bamboo
Boston ferns
Bromelaids
Burros tail succulents
Cast iron plants
Christmas cactus
Echeveria
Gerbera daisies
Orchids
Palms
Poinsettias
Prayer plants
Spider plants
Swedish ivy