Who’s Who in the Citrus Family

What belongs to the genus Citrus?  Oranges, grapefruits, lemons and limes?  But what about citrons, pummelos and kumquats?

Sorting out the citrus family tree has been the job of Robert Krueger, a horticulturalist at the ARS National Clonal Germplasm Repository for Citrus and Dates, in Riverside, California. 

The repository contains a gene bank with specimens of citrus trees, seeds, and pollen.  Krueger and his colleagues have genetically analyzed part of this voluminous collection and found that much of it is basically redundant.

"About 50 of the 400 [specimens] represent more than 90 percent of the collection's true diversity," Krueger said. "That's just 13 percent of the collection."

This supports one theory that most of our grocer's selections - including oranges, grapefruits and lemons - are hybrids, or crosses, of just a few naturally occurring species. 

"Citrus has been domesticated and selected for millennia," Krueger said, "so it's possible that no early ancestors have escaped modification by humankind."

Krueger said there are at least 16 citrus species, with hundreds of distant relatives.

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-- LiveScience Staff

Credit: Peggy Greb