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.
Lumia (citrus)
The most known origin for the Lumia is from the Mediterranean basin. The Lumia is also classified as "Citrus limon var. lumia" by Swingle which places it under the taxonomy of lemon, and "Citrus medica L. var. lumia", that suggests it is similar to citron.