Navel oranges are characterized by the growth of a second fruit at the apex, which protrudes slightly and resembles a human navel. They are primarily grown for human consumption for various reasons: their thicker skin makes them easy to peel, they are less juicy and their bitterness – a result of the high concentrations of limonin and other limonoids – renders them less suitable for juice. Their widespread distribution and long harvest period have made navel oranges very popular.