I had to think about this for a minute. Whenever we talk about tea we are referring to one plant, Camellia sinensis, which may be processed in two major ways to produce the leafy stuff we steep and enjoy. Fermented, or oxidized, it yields the various flavours of black tea such as Earl Grey, Ceylon and Darjeeling. Nonfermented, it produces green tea blends such as Gunpowder or Imperial.
Green tea is more prevalent in the East, while black tea is more common in the West.
Tea is similar to wine in that growing regions and processing can greatly affect its taste and value. Much of the research about the health benefits of tea focuses on this compound. Much of the research on green tea has involved retrospective dietary studies or animal models. While further human studies are needed, the data obtained so far is very promising. Green tea consumption is associated with a lower incidence of cancer.