A member of a group of plants bearing distinctive juicy, acid-tasting fruits of great economic importance. The majority belong to the genus Citrus, but a few come from close relatives. All species are spiny evergreen shrubs or trees; ovoid, dark green, glossy leaves with an articulated joint at the junction of blade and stalk; the stalk often winged, sometimes to the extent of appearing as a second blade attached end-to-end to the first. The leaves of side shoots become modified to form spines. Flowers and fruits are borne on the tree at the same time; the fragrant flowers solitary or in small clusters in the axils of the leaves, with 4–5 sepals and 4–8 white fleshy petals. The fruit is a type of berry, in which the carpels (the familiar segments containing the seeds or pips buried in a pulpy flesh composed of specialized hair-cells) are enclosed in a thick, leathery rind. Both the foliage and rind of the fruit have numerous glands containing aromatic essential oils.
Most Citrus species are cultivated, along with numerous cultivars. They include well-known species such as orange, lemon, lime, grapefruit, as well as more local fruits, such as the shaddock. Citrus fruits originated in China and SE Asia, but have been cultivated in many areas since early times, and a number are of obscure parentage. They are now grown in the tropics and warm temperate regions throughout the world, mainly the Mediterranean, S USA, S Africa, and Australia, and have become a major export crop for several countries. Breeding experiments to produce improved varieties and new and exotic hybrids are common. Although many citrus fruits are grown for eating, either as fresh fruit or in marmalade and preserves, some (eg bergamot orange) are grown for their essential oils, important in the perfume industry. (Genus: Citrus, 12 species. Family: Rutaceae.)
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