Cats need grass to eat. This is cos they lick their fur and that creates a fur-ball obstruction it their stomach. Grass will go around the fur and easier to regurgitate. So I recommend you get a grass plant from one of the nurseries and place this in front position. Other plants are very likely poisons for them and make them very sick. You are lucky that your cat eats the plants. I have given up on plants indoors as they think they are a great toilet!
Aisha-Taweela