But for ARS horticulturalist Robert R. Krueger, the genus Citrus includes at least 16 species, with hundreds of distant relatives, including lesser-known, peelable oddities like pummelos, trifoliate oranges, and kumquats.
Krueger, who is with the ARS National Clonal Germplasm Repository for Citrus and Dates, in Riverside, California, helps look after the nation’s largest collection, or genebank, of citrus trees. The trees, as well as their seeds, budwood, and pollen, serve as valuable germplasm—plant tissue containing the essential genetic information needed to start new citrus plants.
The citrus genebank -- a University of California-Riverside (UCR) resource that is used cooperatively by the ARS repository -- has been gathering accessions for almost a century. Right now its holdings number about 900 specimens, many of which were acquired outside the United States. But it hasn’t been known, until recently, just what the collection’s real breadth and scope were.
“There were redundancies and gaps in the collection that needed to be sorted out,?says Krueger, “and some specimens had even been mislabeled.?Mistakes are costly for curators, since a few missing or added letters can change the way a specimen is classified and managed -- and possibly how it will be used.
“For example, one accession planted in the field,?says Krueger, “was considered to be a Rangpur lime, or Citrus limonia. But when you walked past it, you’d think for sure it was a lemon. It looked like a lemon, smelled like a lemon. Eventually I came by some records from the 1950s indicating that the tree actually was a lemon with the scientific name Citrus limon. Somewhere along the way, someone had mistakenly attached those two letters to the species name.?/p>
A Core Collection
With the h