Navel oranges are distinguished by the development of a second fruit at the apex that resembles a human navel and protrudes slightly. For a variety of reasons, they are primarily grown for human consumption: They are less juicy, have thicker skin, are easier to peel, and are less suitable for juice due to their bitterness and high concentrations of limonin and other limonoids.
Palemon Dorsett, Archibald Dixon Shamel, and Wilson Popenoe of the United States Department of Agriculture (USDA) conducted a study in 1917. They found that between 1810 and 1820, a single mutation in a Selecta orange tree planted on the grounds of a monastery in Bahia, Brazil, probably produced the first navel orange.
The only way to grow navel oranges was to graft cuttings onto other citrus tree varieties because the mutation rendered the fruit seedless, rendering it sterile. The history of navel oranges in Riverside is preserved by the California Citrus State Historic Park and the Orcutt Ranch Horticulture Center.
Navel oranges are still propagated by cutting and grafting today. Because this prevents the usual methods of selective breeding from being used, every navel orange can be considered a fruit of that one, nearly 200-year-old tree: They are clones that share the same genetic makeup as the original tree. This situation is comparable to that of the Cavendish apple, the common yellow seedless banana, or the Granny Smith apple. However, additional mutations may occasionally result in new varieties.