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.
Florentine citron
The source of this variety or hybrid is from the Italian Renaissance gardens. Today it is considered to be a lemon × citron hybrid.