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 plant originally came from Southeast Asia, where it is native. It was spread to the Middle East. Crusaders took it to Europe and North Africa. Spanish explorers took it to the West Indies. This included the Keys in Florida. In 1926, a hurricane destroyed most of the population of commercially-grown limes in region. The Persian lime was reintroduced, then.
Some of the original shrubs grew wild, amongst others, in the Florida Keys. It then became apparent that the originally introduced shrubs (now known as Mexican lime) 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