Black, green, oolong, darjeeling and white tea all come from the same plant, Camellia sinensis. There are two varieties of Camellia sinensis that are grown for tea: Assam which is native to India, and sinensis which is native to China. Tea is grown all over the world, but the majority grown for export comes from China, India, Kenya and Sri Lanka.
The region where the tea is grown, the season and method of harvesting and the processing after harvest all determine the type of tea. For a tea to be called Darjeeling, for example, it must be grown and processed in the Darjeeling region of India. Darjeeling teas are usually, but not always, processed into black or oolong-style tea.
The leaves of the tea plant can be harvested several times throughout the growing season. Typically, it is only the bud and first two leaves on each shoot that are harvested. First flush, second flush and fall flush refer to the time of year in which the leaves were harvested. Tea experts consider the second flush to be the best for quality and flavor, and the fall flush to be inferior to the first and second.
The number of factors that determine the final flavor and quality of a tea are almost limitless. Soil, weather, rainfall, season of harvest, variety of tea plant, drying time, drying temperature, humidity, oxidizing, rolling, firing and storage conditions all play a role.