Fresh lime slices as a background.
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There is nothing like a tangy-sweet slice of key lime pie. But if you are fresh out of key limes, do not make the mistake of trying to substitute regular lime for key lime in a recipe. As much as key limes appear like tiny versions of their relatives, there are quite a few differences that can impact your recipe.

Size of Lime Varieties

If you have ever seen a key lime (Mexican or West Indian) next to a regular lime (Persian or Tahitian), the difference is quite obvious as the varieties of limes vary so widely in size and shape. While Persian limes tend to be slightly smaller than a tennis ball, diminutive key limes are more like the size of a ping-pong ball, about one to one and a half inches in diameter. Persian limes are also heftier than key limes, weighing in at around three ounces, whereas key limes are a featherweight one ounce. Key limes tend to be more rounded as well. Persian or Tahitian limes are more oblong like the shape of a lemon.

Flavor and Aroma

While key limes and Persian limes are similar in flavor, key limes pack a bigger punch of acidity in their small package. Key limes are valued for their "bouquet," or complex aroma, and are widely used around the world to garnish and flavor seafood dishes, add a tangy twist to beverages and impart a zesty quality to otherwise sweet desserts. You can use key limes in salad dressings, drinks, Mexican dishes like guacamole, Thai-inspired chicken dishes or even a ceviche -- raw fish "cooked" by the acid in the lime juice. Key limes work better than Persian limes in cooking because the strong aromatics of the key lime can stand up to cooking and other flavors and scents in a dish. The flavor and acidity cut through other flavors in a dish to help brighten and lift the overall flavor profile.

Tree Varieties

Key lime trees are as small and squat like the key limes they produce. Rarely growing taller than 12 feet, key lime trees tend to be small and bushy with very thorny branches. Leaves are small and pale green with rounded-off tips. Persian lime trees are taller, reaching up to about 15 feet in height, and have no thorns, making harvesting an easier prospect. Their leaves are bright green and serrated. Lime trees are most widely grown in India, China, Mexico, Argentina and Brazil, though they can be grown in other areas and corners of the globe. Key lime trees grow best in Mexico, Florida and California. Again, these trees can grow elsewhere, but these three locations are high producers of the small key limes.

History of Limes in the U.S.

The United States is the worldwide exception in its preference for the larger Persian limes -- the rest of the world prefers the diminutive key limes, instead. The reason for this can actually be traced back to a natural disaster. Up until the early 1900s, key limes were widely cultivated in Florida, but a hurricane in 1926 wiped out the majority of the key lime crop. When the gun-shy farmers replanted, they opted for hardier and more disease-resistant Persian limes, and a new preference was born.