Citrus medica

The citron (Citrus medica) is a large fragrant citrus fruit with a thick, coarse rind. It resembles a lemon, but is larger. It is one of the original citrus fruits from which all other citrus types developed through natural hybrid speciation or artificial hybridization. Though citron cultivars take on a wide variety of physical forms, they are all closely related genetically. It is used in Asian and Mediterranean cuisine, traditional medicines, perfume, and religious rituals and offerings. Hybrids of citrons with other citrus are commercially more prominent, most notably lemons and many limes, which were created using citrons....read more on Wikipedia.