The Key Lime (Citrus aurantiifolia (often, less correctly: C. aurantifolia), or Citrus x aurantiifolia (Christm.) Swingle), also known as the Mexican lime or sometimes as the West Indian lime has a globe shaped fruit, usually 1-2 inches in diameter, that is yellow when ripe but often improperly picked green or unripe commercially. It typically is smaller, has more seeds, and has a higher acidity, a stronger aroma, and a thinner rind than that of the more common Persian lime. It is valued for its unique flavor compared to other limes, with the key lime usually having a more tart and bitter flavor. Named after the Florida Keys, it is best known there as the flavoring ingredient in Key lime pie.
Key Lime trees are generally an easily maintained tree which can reach a height of 16 feet, with many thorns. Dwarf varieties are popular with home growers and can be grown indoors in winter in colder climates. If maintained properly the trunk will grow straight, however, many branches often originate quite far down on the trunk. The leaves are ovate in nature 1–3 inches long, and resemble orange leaves (the scientific name aurantiifolia refers to this resemblance to the leaves of the orange, C. aurantium). The flowers are typically ˝ -3/4 inches in diameter, are yellowish white with a light purple tinge on the margins, and have a very pleasant fragrance. Flowers and fruit appear throughout the year but are most abundant from May to September.
C. aurantiifolia is native to Southeast Asia. Its apparent path of introduction was through the Middle East to North Africa, thence to Sicily and Andalusia and via Spanish explorers to the West Indies, including the Florida Keys. From the Caribbean, lime cultivation spread to tropical and sub-tropical North America, including Mexico, Florida, and later to California.
The English name "lime" was derived from the Persian name Limu in this course. "Key" would seem to have been added some time after the Persian lime cultivar gained prominence commercially in the United States following the hurricane of 1926, which destroyed the bulk of Florida’s C. aurantiifolia agriculture, leaving it to grow mostly casually in the Florida Keys. Since the North American Free Trade Agreement came into effect, many Key limes on the US market are grown in Mexico and Central America.