SYMPTOMS OF PLANT POISONING:

Continual vomiting
Diarrhea
Refusal of food
Pale gums or tongue
Swollen tongue
Abdominal pain
Convulsions

WHAT TO DO IF YOUR CAT IS POISONED:

If your cat experiences any of the above symptoms, consult a veterinarian immediately. Find out what plant your cat got into, as this will help in diagnosing your cat.

PREVENTION:

Whether your cat is outdoor or indoor, always survey the area in which your cat spends his/her time to "kitty-proof". Make sure none of the listed plants are accessible to your cat. It is always best to keep your cat inside.

DANGEROUS HOLIDAY/SEASONAL PLANTS:

American Mistletoe    
Autumn Crocus
Bittersweet
Japanese Euonymus
Holly
Christmas Rose
Crown of Thorns
Poinsettia
Jerusalem Cherry

DANGEROUS COMMON HOUSEPLANTS:

Caladiums
Dumb Cane
Hydrangea
Many indoor Ivies
Ornamental Tobacco
Paperwhites and other winter forced bulbs
Narcissus
 Philodendron 
Rhododendron 

DANGEROUS COMMON OUTDOOR PLANTS:

Clematis 
Cyclamen 
Hydrangea 
Lily 
Narcissus 
Wisteria 
Arrowgrass
Baneberry
Black Locust
Bleeding Heart
Bloodroot
Boston Ivy
Boxwood
Bulb Flowers: Star of Bethlehem, Tulip, Hyacinth, Iris
Buttercup
Castor Bean
Chinaberry
Daphne
Deadly Nightshades (including potato vines, green spots, and tubers)
Dutchman's Breeches
Elderberry
False Hellebore
Foxglove
Jack-in-the-Pulpit
Jimson Weed Thorn Apple
Horse Chestnut
Indian Tobacco
Ground Cherries
Lantana
Larkspur
Delphinium
Lily of the Valley
Locoweed
Lupine Bluebonnet
Monkshood
Morning Glory
Mountain Laurel
Kalmia latifolia
Mushrooms (all outdoor varieties have potential of being toxic)
Oleander
Onions, Chives, other related plants
Poison Hemlock
Poison Oak Poison Ivy
Pokeberry
Poppy
Privet
Rhubarb (only the leaves are toxic)
Rosary Pea
Stinging Nettle
Sweetpea
Tansy Mustard
Tomato (only the vine is toxic)
Virginia Creeper
Wild Cherry, Wild Peach, Wild Apricot, Chokeberry, Almond, Black Cherry
Yews (especially the berries)