Rhobs el Arsa
The Rhobs al Arsa has long been viewed as a citron hybrid, though a different cultivars have been suggested for the parent, for example, Moroccan citron as a male parent and sour orange as the female parent, citron or lemon and a mandarin., or citron and the lime. Detailed genomic analysis has shown Rhobs al Arsa to be highly similar to several cultivars of "Citrus limetta", the limetta or Persian sweet lime, and likely shared a common origin with them, arising from a cross between citron ("Citrus medica") and sour orange ("Citrus" × "aurantium"). The common lemon arose from a distinct hybridization event involving the same two species.
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.