Limes are not unripe lemons. Limes and lemons are two distinct fruits. People erroneously think that limes are unripe lemons because when limes are picked they are fully grown and green in color, but limes left on a tree to the point of being fully ripened would be yellow.
Limes tend to have a higher citric acid and sugar content than lemons. Limes are a good source of vitamin C and are commonly used to enhance the flavor of food and beverages. Limes typically are between 2 and 3 inches in diameter and contain an acidic pulp. The two primary types of limes are Mexican limes and Persian limes. Mexican limes are the ones referred to as Key limes.