Citron
There are also a number of citron hybrids; for example, ponderosa lemon, the lumia and rhobs el Arsa are known citron hybrids, some are claiming that even the Florentine citron is not pure citron, but a citron hybrid.
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.