Citron
A source of confusion is that "citron" or similar words in French (and other languages), and English are false friends, as they refer to the lemon. Indeed, into the 16th century, the English name "citron" included the lemon and perhaps the lime as well.
Citron
Despite the wide variety of forms taken on by the fruit, citrons are all closely related genetically, representing a single species. Genetic analysis has shown known cultivars to divide into three clusters, a Mediterranean cluster thought to have originated in India, and two clusters predominantly found in China, one representing the fingered citrons, and another consisting of non-fingered varieties.