ABSTRACT
The great majority of citrus fruits belong to a most important genus, Citrus, originally of subtropical and tropical areas in eastern Asia, including orange-colored fruits of subtropical background (sour orange, sweet orange, and mandarin) and yellow fruits of tropical background (citron, sour lime, lemon, shaddock, and grapefruit). The number of species of this genus is highly controversial, ranging between 16 and 157. 12 As in other apomictic types, linnean taxonomy does not really apply (because of the ease of free intercrossing followed by perpetuation of types through nucellar embryony). Lately, it has been proposed 3 that only three true species originally existed (see Table 1), and they yielded all other “species” by intercrossing among themselves and with a close relative, the genus Microcitrus. Two other genera, Fortunella spp. and Poncirus trifoliata, are usually included in citrus fruits.
