Standard lime juice is a kitchen staple. Key lime juice, however, comes from a unique fruit tree and is more rare. Of course it's known for one of Florida's most famous desserts, the key lime pie.
Persian Limes
The typical, bright green grocery-store lime is also known as the Persian lime. A little known fact—they actually become yellow when fully ripe but are sold only when they're still green.
Key Limes
The key lime is native to Asia and was brought to the Florida Keys by the Spanish in the 1500s. A hurricane in 1926 destroyed most of Florida’s key-lime plantations, so today most of the commercial crop is grown elsewhere.
Differences in Appearance
Key limes are smaller and contain more seeds than Persian limes. Persian limes have a thick, vividly green skin, while key lime skin is thin and yellowish.
Differences in Taste
Key lime juice is more aromatic and intense than that of the Persian lime.
Availability
Persian limes and lime juice are available in grocery stores all year. It can be difficult to find fresh key limes because they're in shorter supply and don't stay fresh as long. However, bottled key lime juice is available in specialty and online stores.