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Black tea is made from the dried leaves of Camellia sinensis , a perennial evergreen shrub. Black tea has a long history of use dating back to China approximately 5,000 years ago. Green tea, black tea, and oolong tea are all derived from the same plant. Black tea is a source of caffeine, a methylxanthine that stimulates the central nervous system, relaxes smooth muscle in the airways to the lungs (bronchioles), stimulates the heart, and acts on the kidney as a diuretic (increasing urine). One cup of tea contains about 50 milligrams of caffeine, depending on the strength and size of cup (as compared to coffee, which contains 65 to 175 milligrams of caffeine per cup). Tea also contains polyphenols (catechins, anthocyanins, phenolic acids), tannin, trace elements, and vitamins. The tea plant is native to Southeast Asia and can grow up to a height of 40 feet, but is usually maintained at a height of two to three feet by regular pruning. The first spring leaf buds, called the first flush , are considered the highest-quality leaves. When the first flush leaf bud is picked, another one grows, which is called the second flush , and this continues until an autumn flush . The older leaves picked farther down the stems are considered to be of poorer quality. Tea varieties reflect the growing region (for example, Ceylon or Assam), the district (for example, Darjeeling), the form (for example, pekoe is cut, gunpowder is rolled), and the processing method (for example, black, green, or oolong). India and Sri Lanka are the major producers of black tea. Historically, tea has been served as a part of various ceremonies and has been used to stay alert during long meditations. A legend in India describes the story of Prince Siddhartha Gautama, the founder of Buddhism, who tore off his eyelids in frustration at his inability to stay awake during meditation while journeying through China. A tea plant is said to have sprouted from the spot where his eyelids fell, providing him with th...