Citron, a subtropical citrus tree, native to Asia. The fruit has a thick, fragrant rind that is candied and used in cakes and confections. The tree is cultivated in Puerto Rico, in southern Europe, and to a small extent in Florida and California. It is a small evergreen that grows to be about 10 feet (3 m) tall. It has toothed leaves and purple flowers. The fruit, 4 to 10 inches (10 to 25 cm) long, is yellow and shaped like a lemon.
The citron melon is not related to the citron tree; it is a variety of watermelon.
The citron tree is Citrus medica of the rue family, Rutaceae.