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.
Diamante citron
While Calabria is at the southern point of Italy, and its climate most Mediterranean, it is the most suitable for the citron. Even though, during the winter it is still too cold for the citron; this is why the farmers need to protect them with blue or green plastic covers. Most of the citron trees in the area are grafted onto foreign citrus rootstock, in order to save them from frost and disease. This practice renders their fruits non-kosher for the Sukkot ritual, and therefore in order for a mashgiach to certify a citron as kosher, he must first carefully inspect the tree to confirm it was not grafted.