Cats are strict meateaters (carnivores), so foraging on plant material has no nutritional value for them. It is probably done to stimulate the vomiting reflex as a means to get rid of hairballs. There are exceptions to the rule … my cat Jackson, for example, loves to eat cantaloupe.
Most houseplants, if foraged on by cats, produce nothing more than a simple stomach upset. Some houseplants, however, are toxic, especially those that we may bring into our homes around the Holidays – particularly mistletoe and the poinsettia. Mistletoe contains a substance that can cause severe nausea, cramping, vomiting, and diarrhea. The poinsettia plant produces a milky sap that is a chemical irritant. Direct contact with the sap can cause stomatitis, gastritis, as well as conjunctivitis.
Of the common household potted plants found in the home, those in the family Araceae, such as philodendron, dumb canes, and elephant ears, can cause histamine poisoning. Clinical signs would include intense salivation, breathing difficulties, and loss of voice due to edema of the vocal cords.