For eight years, Jill Richardson, D.V.M., was the voice of safety at the ASPCA Animal Poison Control Center in Urbana, Ill. She fielded calls from frantic owners worried that their dogs had eaten a toxic leaf, stem, or flower.

To protect her own dogs, Richardson made certain that poisonous plants never made their way into her Urbana home or her yard's landscape. "People are often surprised to learn that there are actually hundreds of plants potentially poisonous to dogs," says Richardson, who left the ASPCA to become associate director of consumer relations for Hartz Mountain Corp. in Secaucus, N.J.

Richardson identifies the top 10 most common poisonous houseplants and landscape plants dog owners should avoid:

Autumn crocus (Colchicum): Its active ingredient, colchicines, triggers an anti-metabolic effect that can cause rapidly dividing cells, shedding of the gastrointestinal tract, bloody diarrhea, and vomiting.

Azalea (Rhododendron): This popular plant can harm a dog's cardiovascular system and trigger vomiting or gastrointestinal upset.

Daffodil (Narcissus): Toxic ingredients in the bulbs cause convulsions, tremors, lethargy, weakness, and upset stomachs.

Hyacinth (Hyacinth): This popular plant can cause severe vomiting, bloody diarrhea, depression, and tremors.

Japanese yew (Taxis): Extremely toxic to dogs, this group of ornamental plants can cause seizures or cardiac failure. The plant and red berries are toxic.

Lily of the valley (Convalaria): This plant can cause heart failure, coordination problems, and vomiting.

Oleander (Nerium): Extremely toxic, this popular outdoor plant contains cardiac glycosides that harm the heart, decrease body temperature, cause abnormal pulse rate, and can cause death. Beware: Even people have died from eating hot dogs roasted on an oleander twig.

Rhubarb (Rheum): Although the stalks are used to make pies, the leaves pack the potential to cause kidney damage.

Sago palm (Cycads): Resembling an upside down pineapple, this plant thrives in sandy soils, especially in warmer states such as California, Texas, and Florida. A few seeds can kill a dog.

Tomato (Lycopersicion): Surprisingly, the greenery of this common plant, not the tomato itself, contains solanine, a toxic ingredient that can prompt gastric upset, depression, weakness, and a decrease in heart rate.

Richardson's parting advice: Keep your dog away from any mushrooms. "Always assume any ingested mushroom by a dog is toxic and will cause liver failure," Richardson says. "The problem is that many poisonous mushrooms often grow together with non-poisonous mushrooms."

For more information on poisonous plants, tap into the ASPCA Animal Poison Control Center or the American Veterinary Medical Association website.