Citrus

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.