All tea comes from the Camellia sinensis plant, a warm-weather evergreen. How the fresh leaves of the tea plant are processed and their level of contact with oxygen (process known as oxidation) determine resulting types of tea. During oxidation, tea leaves undergo natural chemical reactions that result in distinctive color and taste characteristics. Green tea is not oxidized at all the leaves are steamed, rolled and dried while black tea is allowed to oxidize for two to four hours. Oolong tea falls somewhere between green and black teas, in that the leaves are only partially oxidized.