Camellia sinensis
Camellia sinensis is the tea plant, the plant species whose leaves and leaf buds are used to produce tea. It is of the genus Camellia (Chinese: ; pinyin: Chahua), a genus of flowering plants in the family Theaceae. White tea, green tea, oolong and black tea are all harvested from this species, but are processed differently to attain different levels of oxidation. Kukicha (twig tea) is also harvested from camellia sinensis, but uses twigs and stems rather than leaves.
The name sinensis means Chinese in Latin. Camellia is taken from the Latinized name of Rev. Georg Kamel, S.J. (1661-1706), a Czech-born Jesuit priest who became both a prominent botanist and a missionary to the Philippines (it is not uncommon for members of the Catholic Jesuit order to combine careers in scholarship with their religious work). Though Kamel did not discover or name the plant, Karl von Linnaeus, the creator of the system of taxonomy still used today, chose his name for the genus of this tree to honor Kamel's contributions to science. Older names for the tea plant include Thea bohea, Thea sinensis and Thea viridis.

# Description
Camellia sinensis is native to mainland South and Southeast Asia, but is today cultivated across the world, in tropical and subtropical regions. It is an evergreen shrub or small tree that is usually trimmed to below two metres (six feet) when cultivated for its leaves. It has a strong taproot. The flowers are yellow-white, 2.54 cm in diameter, with 7 to 8 petals.
The seeds of Camellia sinensis and Camellia oleifera can be pressed to yield tea oil, a sweetish seasoning and cooking oil that should not be confused with tea tree oil, an essential oil that is used for medical and cosmetical purposes and originates from the leaves of a different plant.
The leaves are 415 cm long and 25 cm broad. Fresh leaves contain about 4% caffeine. The young, light green leaves are preferably harvested for tea production; they have short white hairs on the underside. Older leaves are deeper green. Different leaf ages produce differing tea qualities, since their chemical compositions are different. Usually, the tip (bud) and the first two to three leaves are harvested for processing. This hand picking is repeated every one to two weeks.
The three most common types of tea are green, oolong and black (others include yellow, white, compressed and flavoured teas).  All use the same leaves of the same plant. Green tea is steamed (Japanese method) or roasted (Chinese method) very soon after picking to stop the oxidation process.  Oolong tea is left to oxidize a bit longer and is the type used by most Chinese restaurants.  Black tea is oxidized for the longest period of time which produces the darkest of the teas. White tea, a delicacy in the orient now beginning to be found in Western shops, is made from "tea needles," the newest, still folded shoots of leaves at the end of branches. Further distinctions are made to denote the size of the leaves used (the youngest, smallest leaves are generally held to have the highest quality flavor), and the region of origin (in much the same way wine is classified).

# Cultivation
Main article: Tea cultivation.
Camellia sinensis is mainly cultivated in tropical and sub-tropical climates, in areas with at least 50 inches of rainfall a year. 
However, it is commercially cultivated from the equator to as far north as  Cornwall on the UK mainland. Many high quality teas are grown at high elevations, up to 1500 meters (5,000 ft), as the plants grow more slowly and acquire a better flavor.
Tea plants will grow into a tree if left undisturbed, but cultivated plants are pruned to waist height for ease of plucking. Two principal varieties are used, the small-leaved Chinese variety plant (C. sinensis sinensis) and the large-leaved Assamese plant (C. sinensis assamica), used mainly for Black tea.

# Varieties
Several varieties of C. sinensis are used for tea production:

## Assamese variety
The most volume comes from the Assam variety (sometimes called C. sinensis var. assamica or C. assamica), predominantly grown in the Assam region. It is a small tree (single stemmed) with large leaves. In the wild it reaches a height of 6 to 20 meters (2065 feet) and is native to north-east India, Myanmar, Vietnam, and south China. In tea estates it is kept trimmed to just above waist level. A lowland plant, it requires a high rainfall but good drainage. It does not tolerate extreme temperatures. Discovered in 1823 (though used earlier by local people in their brews), it is one of the two original tea plants. All Assam teas and most Ceylon teas are from this plant. The Assam plant produces malty, earthy drinks, unlike the generally flowery yield of the China plant.

## Chinese variety
The Chinese plant (sometimes called C. sinensis var. sinensis) is a small-leaved bush with multiple stems that reaches a height of some 3 meters. It is native to south-east China. The first tea plant to be discovered, recorded and used to produce tea three thousand years ago, it yields some of the most popular teas.
C. sinensis var. waldenae was considered a different species, Camellia waldenae by S.Y.Hu, but it was later identified as a variety of C. sinensis. This variety is commonly called Walden's Camellia. It is seen on Sunset Peak and Tai Mo Shan in Hong Kong. It is also distributed in Giangxi Province, China.

## Cambodian variety
The Cambodian plant is sometimes called C. sinensis var. parvifolia. Its leaves are in size between the Assam and Chinese varieties; it is a small tree with several stems. It is sometimes referred to as a hybrid of the Assam and China plants.

## Diseases

# Medical uses
- The leaves have been used in traditional Chinese medicine (TCM), and other medical systems to treat asthma, bronchodilator, angina pectoris, peripheral vascular disease, and coronary artery disease.
Tea extracts have become field of interest, due to their notional antibacterial activity. Especially the preservation of processed organic food and the treatment of persistent bacterial infections are being investigated.
- Green tea leaves and extracts have shown to be effective against bacteria responsible for bad breath.
- The tea component epicatechin gallate is being researched because in-vitro experiments showed that it can reverse methicillin resistance in bacteria like Staphylococcus aureus. If confirmed, this means that the combined intake of a tea extract containing this component will enhance the effectiveness of methicillin treatment against some resistant bacteria.