Citrus

In general, three Citrus ancestral species (pomelos, citrons, and papedas) synthesize relatively high quantities of furanocoumarins, whereas a fourth ancestral species (mandarins) is practically devoid of these compounds.[46] Since the production of furanocoumarins in plants is believed to be heritable, the descendants of mandarins (such as sweet oranges, tangerines, and other small mandarin hybrids) are expected to have low quantities of furanocoumarins, whereas other hybrids (such as limes, grapefruit, and sour oranges) are expected to have relatively high quantities of these compounds.

In one comprehensive study of 61 Citrus varieties,[46] two papedas (Citrus micrantha and Citrus hystrix) had the highest concentrations of furanocoumarins of any Citrus species (even more than the bergamot), in both the peel and the pulp. The study also found high furanocoumarin content in the peel of lime and bergamot, and in the pulp of pomelo, grapefruit, and sour orange. These results are consistent with what is already known, that is, lime and bergamot lead to phytophotodermatitis, while pomelo and grapefruit are involved in grapefruit-drug interactions.

In most Citrus species, the peel contains a greater diversity and a higher concentration of furanocoumarins than the pulp of the same fruit.[47][48][46] An exception is bergamottin, a furanocoumarin implicated in grapefruit-drug interactions, which is more concentrated in the pulp of certain varieties of pomelo, grapefruit, and sour orange.

The genus Citrus has been suggested to originate in the eastern Himalayan foothills. Prior to human cultivation, it consisted of just a few species, though the status of some as distinct species has yet to be confirmed:

• Citrus crenatifolia – species name is unresolved, from Sri Lanka


• Citrus japonica – kumquats, from East Asia ranging into Southeast Asia (sometimes separated into four-five Fortunella species)


• Citrus mangshanensis – species name is unresolved, from Hunan Province, China


• Citrus maxima – pomelo (pummelo, shaddock), from the Island Southeast Asia


• Citrus medica – citron, from India


• Citrus platymamma – byeonggyul, from Jeju Island, Korea


• Citrus reticulata – mandarin orange, from China


• Citrus trifoliata – trifoliate orange, from Korea and adjacent China (often separated as Poncirus)


• Australian limes
  


• Papedas, including
  

Hybrids and cultivars[edit]