Important hybrids: Citrus × aurantium – Bitter Orange Citrus × latifolia – Persian Lime Citrus × limon – Lemon Citrus × limonia – Rangpur Citrus × paradisi – Grapefruit Citrus × sinensis – Sweet Orange See also below for other species and hybrids.

Eremocitrus Microcitrus and see text

Citrus is a common term and genus of flowering plants in the family Rutaceae, originating in tropical and subtropical southeast regions of the world. The Latin word citrus was borrowed from ancient Greek kedros "cedar, juniper" probably through Etruscan. The Romans applied the word to several different trees with fragrant foliage or wood (compare the completely unrelated cedars). The taxonomy and systematics of the genus are 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 some wild, true-breeding species are of hybrid origin. Cultivated Citrus may be derived from as few as four ancestral species. Natural and cultivated origin hybrids include commercially important fruit such as the oranges, grapefruit, lemons, some limes, and some tangerines.

Research suggests that the closely related genus Fortunella (kumquats), and perhaps also Poncirus and the Australian Microcitrus and Eremocitrus, should be included in Citrus; most botanists now classify Microcitrus and Eremocitrus as part of the genus Citrus.