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.
Citrin
The term Citrin when referring to Vitamin-P was the most active Bio-flavonoid in lemons, it was found to be Eriodictyol (but a more active form constituent was found there decades later).