Yerba maté is not prepared from the tea plant, but from a plant called Ilex paraguariensis, which contains caffeine and other xanthines. Maté is a traditional beverage throughout South America, typically served hot and shared among friends from a gourd. It is typically steeped in hot (not boiling) water.
These teas have flavorings, herbs, or other ingredients added to them. Basically all of our herbal teas can be considered "flavored."