What is a navel orange?

By Chelsie Vandaveer

February 13, 2003

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The orange is not a species; no wild type has been discovered. Oranges, both sour and sweet, do escape from cultivation and grow in the wild, but there was no original wild orange. The designation for the sweet orange, Citrus sinensis Osbeck, is a name of convenience used in horticulture and agriculture. (It is shunned by most taxonomists.) Linnaeus's designation—Citrus X aurantium—belongs to sour and sweet oranges, as well as grapefruit, indicating hybrid status. The orange is now believed a cross between a pomelo (Citrus maxima) and a tangerine (C. reticulata).

Dwarf Navel Orange Citrus sinensis 'Washington Navel'—Produces seedless three inch fruit mid-fall to mid-spring, fragrant white flowers in summer. Click here - Save $20 on $50 order [More Fruit]

The problem with naming the species within the genus Citrus comes from the plants. All Citrus have 18 chromosomes (n=9) and are interfertile. Oranges are probably cultivars, plants that came into being under cultivation. The hybridization may have taken place in the wild and some smart gardener recognized a good thing, or the tree resulted from cross-pollination because of close proximity to other Citrus in a garden.

But Citrus trees also "bud-sport", produce a mutated bud that when grown into a branch will have fruit or other characteristics different from the parent on which it is growing. Most mutations are undesirable, the Citrus fruit, a berry properly called a hesperidium, reverts toward the inedible—bitter, small, or mostly rind.

The navel orange is a bud-sport of the sweet orange. The mutation happened in a garden at a monastery in Bahia, Brazil around 1820. This particular mutation caused a doubling of the berry. Navel orange flowers produce little viable pollen; they do not need pollination to set the hesperidia. Seeds never develop and the ovary becomes a second rudimentary berry found within the orange at the apical end where the blossom was attached—the "navel" in the orange.

The Horticulture Department of Texas A & M University has a great photograph of navel oranges. The orange on the right shows the secondary berry at the blossom end of the hesperidium. To view the photograph, click on the link:

http://aggie-horticulture.tamu.edu/citrus/cultivars/navel.htm

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