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.
Meyer lemon
Citrus" × "meyeri, the Meyer lemon, is a hybrid citrus fruit native to China. It is a cross between a citron and a mandarin/pomelo hybrid distinct from the common or bitter oranges.