Every Navel Orange comes from the same tree — sort of:
A single mutation in 1820 in an orchard of sweet oranges planted at a monastery in Brazil yielded the navel orange, also known as the Washington, Riverside or Bahia navel. The mutation caused each fruit on the tree to develop as a set of “siamese twins”, with a smaller orange embedded in a larger one opposite the stem. From the outside, the smaller, undeveloped twin left a formation at the bottom of the fruit, looking similar to the human navel.
Because the mutation left the fruit seedless and therefore sterile, the only means available to cultivate more of this new variety is to graft cuttings onto other varieties of citrus tree. Two such cuttings of the original tree were transplanted to Riverside, California in 1870, which eventually led to worldwide popularity.
Today, navel oranges continue to be produced via cutting and grafting. This does not allow for the usual selective breeding methodologies, and so not only do the navel oranges of today have exactly the same genetic makeup as the original tree, they can even be considered to all be the fruit of that single, now centuries-old tree.