The tea plant, Camellia sinensis, is an evergreen shrub which in the wild, can reach tree-like heights. On farms, tea is generally pruned into bushes of convenient picking height (two to four feet). The bark of the plant is rough and slightly gray; the leaves are serrated, dark green and elliptical, and formed on short stalks. The buds have a light downy covering, prized in certain high-quality teas, and occasionally, small white flowers are present. Seeds are contained within a smooth, round, three-celled hull, like a small nut. The new growth—the top two leaves and/or the bud—is the part which is harvested, as the best flavor and fragrance are concentrated here.
Tea originated in southeastern Asia, growing in a broad swath across modern-day Yunnan Province (China), Laos, Burma and eastern Assam (India). Cultivation of the plant Camellia sinensis var. sinensis began around 4,000 years ago in Sichuan Province, China, then spread throughout that country. It then moved into Japan in the 800s, and Taiwan in the mid 1800s. Around 1830, the tea industry was established in the then-British colony of Assam, and the Dutch colony of Sri Lanka a few decades later. In Assam, the native Camellia sinensis var. assamica was also discovered, which is the second major variety of the tea plant. This assamica variety has large leaves and thrives in the low plains of India and jungles of Yunnan; the sinensis variety, which has small leaves, is better suited to higher elevations and a tougher climate. Today, most tea plants are a cultivars of these two genetic varieties.
All tea hails from the same Camellia sinensis plant; the five different types of tea—white, green, oolong, black, pu-erh—are defined by how the leaf is processed, and the cultivars used. While tea is now grown in significant commercial quantities on every continent except Europe and North America, the countries for traditional looseleaf tea production remain China, Japan, Taiwan, India and Sri Lanka.
Chemically, tea leaves contain natural plant compounds such as polyphenols (catechins, tannins and flavonoids—the source of antioxidants) and alkaloids (caffeine, theobromine, theophylline). Tea's unique combination of caffeine and the rare amino acid theanine—found in only one other plant besides Camellia sinensis—yield a drink that is both envigorating and relaxing. Theanine's calming property is especially notable for its corresponding lack of sedative effects.