The key lime (Citrus aurantifolia Swingle) is a smaller, more fragrant cousin of the common Persian lime. Ranging in size from just 1 to 2 inches (2.5 to 5 cm) in diameter, key limes are a good deal smaller than other limes.
The key lime distinguishes itself in ways other than size. Its rind, slightly thinner and more delicate than that of the larger Persian variety, is lighter and yellowish green in color. Key limes are more acidic, have a greater number of seeds, and also have a more distinctive aroma than the larger limes. These qualities make key limes prized for their culinary contributions, especially to their namesake, the key lime pie.
Key limes grow on a rather thorny, bushy tree that maintains a fairly petite height at maturity of about 12 to 16 feet (4 to 5 m). There are also dwarf varieties of the tree available for container growing. The branches and trunk of the key lime tree assume a somewhat shrubby configuration, with branches growing not just at the crown of the tree but fairly far down the trunk as well. The leaves of the key lime are oval and light green, and the blossoms are yellow-white with pale purple accents on the edges.
The key lime is highly sensitive to cold, and requires a great deal of direct sunlight. It is not picky about soil, other than that it requires good drainage. The key lime tree will bear fruit year-round under ideal conditions, but it is most prolific in the late spring through early fall.
The key lime is believed to have originated in Southeast Asia, traveling through the Middle East to Sicily and Spain and eventually to the New World via the West Indies and the Florida Keys by way of explorers from Spain. From there, cultivation spread through suitable regions of North America.
Key limes are available fresh in stores year-round, and the juice of key limes may be purchased in bottles. Key limes are an excellent source of vitamin C, and enhance the flavor of many foods, including chicken, fish, shellfish, and other seafood. Key lime juice adds a brightly tart note to salad dressings, marinades, cocktails, and fruit juices, and, of course, key limes star in the renowned key lime pie.
When choosing key limes, look for smooth, unblemished skins that are yellowish green with no brown patches. The limes should have a good weight for their size. Key limes may be stored at room temperature for a few days or kept in a plastic bag in the refrigerator for up to two weeks. For longer storage, squeeze the limes and freeze the juice in ice cube trays. Store the frozen cubes in resealable plastic bags in the freezer.