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.
Mandarin orange
According to molecular studies, the mandarin, the citron, the pomelo, and to a lesser extent the papedas and kumquat, were the ancestors of most other commercial citrus varieties, through breeding or natural hybridization; mandarins are therefore important as the only sweet fruit among the parental species. Though some mandarin cultivars remain pure, most have some degree of pomelo hybridization, while in some cases the amount of pomelo is substantial.