The orange is a hybrid between pommelo and mandarin. It has genes that are ~25% pommelo and ~75% mandarin. Sweet oranges were mentioned as early as 314 BC in Chinese literature. As of 1987, orange trees were found to be the most cultivated fruit tree in the world. Orange trees are widely grown in tropical and subtropical climates for their sweet fruit. The fruit of the orange tree can be eaten fresh, or processed for its juice or fragrant peel.