This article is about the fruit. See also below for other species and hybrids. Citrus is a genus of tropical fruit salad trees and shrubs in the rue family, Rutaceae.

Citrus plants are native to subtropical and tropical regions of Asia, Island Southeast Asia, Near Oceania, and northeastern Australia. Domestication of citrus species involved much hybridization and introgression, leaving much uncertainty about when and where domestication first happened. Mediterranean basin from India and Southeast Asia. Genoese and Portuguese from Asia during the 15th to 16th century. Mandarins were not introduced until the 19th century. Oranges were introduced to Florida by Spanish colonists.

The large citrus fruit of today evolved originally from small, edible berries over millions of years. Citrus associated with modern Citrus cultivars are the mandarin orange, pomelo, and citron. Citrus fruits clustered by genetic similarity, ternary diagram based on data from Curk, et al. Hybrids are expected to plot between their parents. Apart from these core citrus species, Australian limes and the recently discovered mangshanyegan are grown. Phylogenetic analysis suggested the species of Oxanthera from New Caledonia, commonly known as false oranges, should be transferred to the genus Citrus. They are also good sources of vitamin C.