If not, they are called races, which means that a formal rank should not be given to the group, or taxonomists are unsure whether or not a formal rank should be given.
The key lime is a shrub that grows to a size of about 5 metres in height. It has many thorns. It produces a fruit that is yellow when it is ripe. This fruit is preferred by bartenders to mix cocktails. They prefer this lime, rather than the Persian lime.
The lime plant originally came from southeast Asia, where it is native. It was taken to the Middle East, and Crusaders took it to Europe and North Africa. Spanish explorers took it to the West Indies and the Florida Keys. In 1926, a hurricane destroyed most of the commercially-grown limes in the region. The Persian lime was reintroduced then.
Some of the original shrubs grew wild in the Florida Keys. It became clear that the originally introduced shrubs (now known as Mexican limes) had modified their fruits. These were darker green than the original Persian limes, they also had a thicker skin.
- Ernst Mayr (1970). Populations, species, and evolution : an abridgment of Animal species and evolution. Cambridge, Mass: Belknap Press. ISBN 0-674-69013-3.
- Mayr, Ernst 2002. The biology of race and the concept of equality. Daedalus, Winter 2002, 89-94. 
- Morton J. 1987. Mexican lime, p.168–172. In: Fruits of warm climates. Julia F. Morton, Miami, FL. Citrus aurantiifolia Swingle