Species Citrus aurantifolia—Key lime Citrus maxima—Pomelo Citrus medica—Citron Citrus reticulata—Mandarin & Tangerine Major hybrids Citrus ×sinensis—Sweet Orange Citrus ×aurantium—Bitter Orange Citrus ×paradisi—Grapefruit Citrus ×limon—Lemon Citrus ×limonia—Rangpur lime Citrus ×latifolia—Persian lime See also main text for other hybrids
Citrus is a common term and genus of flowering plants in the family Rutaceae, originating in tropical and subtropical southeast Asia. The plants are large shrubs or small trees, reaching 5–15 m tall, with spiny shoots and alternately arranged evergreen leaves with an entire margin. The flowers are solitary or in small corymbs, each flower 2–4 cm diameter, with five (rarely four) white petals and numerous stamens; they are often very strongly scented. The fruit is a hesperidium, a specialised berry, globose to elongated, 4–30 cm long and 4–20 cm diameter, with a leathery rind surrounding segments or "liths" filled with pulp vesicles. The genus is commercially important as many species are cultivated for their fruit, which is eaten fresh or pressed for juice.
Citrus fruits are notable for their fragrance, partly due to flavonoids and limonoids (which in turn are terpenes) contained in the rind, and most are juice-laden. The juice contains a high quantity of citric acid giving them their characteristic sharp flavour. They are also good sources of vitamin C and flavonoids.
The taxonomy of the genus is complex and the precise number of natural species is unclear, as many of the named species are clonally-propagated hybrids, and there is genetic evidence that even the wild, true-breeding species are of hybrid origin. Cultivated Citrus may be derived from as few as four ancestral species. Numerous natural and cultivated origin hybrids include commercially important fruit such as the orange, grapefruit, lemon, some limes, and some tangerines. Recent research has suggested that the closely related genus Fortunella, and perhaps also Poncirus and the Australian genera Microcitrus and Eremocitrus, should be included in Citrus. In fact, most botanists now classify Microcitrus and Eremocitrus as part of the genus Citrus.

Pests and diseases

Uses
Many citrus fruits, such as oranges, tangerines, grapefruits, and clementines, are generally eaten fresh. They are typically peeled and can be easily split into segments. Grapefruit is more commonly halved and eaten out of the skin with a utensil. Orange and grapefruit juices are also very popular breakfast beverages. More astringent citrus, such as lemons and limes are generally not eaten on their own. Though 'Meyer' "Lemon" can be eaten 'out of hand', it is both sweet and sour. Lemonade or limeade are popular beverages prepared by diluting the juices of these fruits and adding sugar. Lemons and limes are also used as garnishes or in cooked dishes. Their juice is used as an ingredient in a variety of dishes, it can commonly be found in salad dressings and squeezed over cooked meat or vegetables. A variety of flavours can be derived from different parts and treatments of citrus fruits. The rind and oil of the fruit is generally very bitter, especially when cooked. The fruit pulp can vary from sweet and tart to extremely sour. Marmalade, a condiment derived from cooked orange and lemon, can be especially bitter. Lemon or lime is commonly used as a garnish for water, soft drinks, or cocktails. Citrus juices, rinds, or slices are used in a variety of mixed drinks. The skin of some citrus fruits, known as zest, is used as a spice in cooking. The zest of a citrus fruit, preferably lemon or an orange, can also be soaked in water in a coffee filter, and drank.

Culinary
Citrus juice also has medical uses - the lemon juice is used to relieve the pain of bee stings. The orange is also used in Vitamin C pills, which prevents scurvy. Scurvy is caused by Vitamin C deficiency, and can be prevented by having 10 milligrams of Vitamin C a day. An early sign of scurvy is fatigue. If ignored, later symptoms are bleeding and bruising easily.

History

Alemow, Colo, C. ×macrophylla
Amanatsu
Bergamot orange C. ×bergamia
Bitter orange, Seville Orange
Blood orange
Buddha's hand, C. medica
Calamondin (Calamansi)
Citron Citrus medica
Clementine
Daidai, Seville, Sour Orange, Citrus aurantium
Dekopon- hybrid between ChungGyun mandarins and Ponkan
Desert Lime, Citrus glauca (syn. Eremocitrus glauca)
Djeruk limau, C. ×amblycarpa, Indonesia
Finger Lime, Citrus australasica, (syn. Microcitrus australasica)
Gajanimma, Carabao lime, C. ×pennivesiculata
Grapefruit, C. ×paradisi
Ichang Lemon Citrus ×ichangensis
Imperial lemon Citrus limon × Citrus ×paradisi
Iyokan
Kabosu Citrus sphaerocarpa
Kaffir lime Citrus ×hystrix
Key lime Citrus aurantifolia
Kinnow
Khasi pepeda, C. ×latipes
Kumquat - in the related genus Fortunella, not Citrus; forms hybrids with Citrus (see Citrofortunella)
Lemon Citrus ×limon
Lime Citrus aurantifolia
limetta, Sweet Lemon C. ×limetta
Limequat Citrus ×Fortunella hybrids
Mandarin Lime C. ×limonia
Mandarin Orange, Dancy
Meyer Lemon
Mikan
Natsumikan, Japan, C. ×natsudaidai
Orange Citrus sinensis
Orangelo: Chironja
Orangequat
Oroblanco
Persian lime, Tahiti lime Citrus ×latifolia
Pomelo, Pummelo, Shaddock, Citrus grandis
Ponderosa lemon
Ponkan
Rangpur, Lemanderin Citrus ×limonia
Rough Lemon C. ×jambhiri
Satsuma
Shekwasha, Taiwan tangerine, Hirami lemon, C. ×depressa
Sudachi
Sunki, Suenkat, C. ×sunki
Sweetie
Sweet Lime, Sweet Lime, Central America, C. ×limettioides
Tachibana Orange
Tangelo: Minneola tangelo Ugli
Tangerine Citrus reticulata
Tangor C. ×nobilis
Ugli fruit
Yuzu C. ×junos