Citrus is a common term and genus of flowering plants in the rue family, Rutaceae.
The taxonomy of the genus is complex and the precise number of natural species is unclear, as many of the names species are clonally propagated hybrids. Some wild, true-breeding species are of hybrid species. Cultivated Citrus may be derived from as few as 4 ancestral species.
Citrus has been suggested to originated in S.E.Asia. Prior to human cultivation, it consisted of just few species : C. aurantifolia. C. maxima (柚), C. medica, C. reticulata (柑，橘), C. tifoliata / Poncirus trifolia (枳), C. australasica, C. australis, C. glauca, C. japonica / Fortunella japonica, C. halimii, C. indica, etc