page_title: Citrus taxonomy
section_title: Graft hybrids
hierarchical_section_title: Citrus taxonomy / Graft hybrids
caption_attribution_description: Citrus aurantium "bizzarria" frutto acerbo
context_page_description: Citrus taxonomy refers to the botanical classification of the species, varieties, cultivars, and graft hybrids within the genus Citrus and related genera, found in cultivation and in the wild.
  Citrus taxonomy is complex. Cultivated citrus are derived from various citrus species found in the wild. Some are only selections of the original wild types, while others are hybrids between two or more ancestors. Citrus plants hybridize easily between species with completely different morphologies, and similar-looking citrus fruits may have quite different ancestries. Some differ only in disease resistance. Conversely, different-looking varieties may be nearly genetically identical, and differ only by a bud mutation.
  Detailed genomic analysis of wild and domesticated citrus cultivars has suggested that the progenitor of modern citrus species expanded out of the Himalayan foothills in a rapid radiation that has produced at least 10 wild species in South and East Asia and Australia. Most commercial cultivars are the product of hybridization among these wild species, with most coming from crosses involving citrons, mandarins and pomelos.
context_section_description: Due to the sterility of many of the genetic hybrids as well as disease- or temperature-sensitivity of some Citrus trees, domesticated citrus cultivars are usually propagated via grafting to the rootstock of other, often hardier though less palatable citrus or close relatives.  As a result, graft hybrids, also called graft-chimaeras, can occur in Citrus.  After grafting, the cells from the scion and rootstock are not somatically fused, but rather the cells of the two intermix at the graft site, and can produce shoots from the same tree that bear different fruit.  For example, the 'Faris' lemon, has some branches with purple immature leaves and flowers with a purple blush that give rise to sour fruit, while other branches produce genetically-distinct sweet lemons coming from white flowers, with leaves that are never purple.  Graft hybrids can also give rise to an intermixed shoot that bears fruit with a combination of the characteristics of the two contributing species due to the presence of cells from both in that fruit.  In an extreme example, on separate branches Bizzaria produces fruit identical to each of the two contributing species, but also fruit that appears to be half one species and half the other, unmixed.  In taxonomy, graft hybrids are distinguished from genetic hybrids by designating the two contributing species with a '+' between the individual names (Citrus medica + C. aurantium).
caption: Bizzaria, an unusual graft-chimera.
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