Citron
The citron ("Citrus medica") is a large fragrant citrus fruit with a thick rind. 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 widely in Asian cuisine, and also in traditional medicines, perfume, and for religious rituals and offerings. Hybrids of citrons with other citrus are commercially prominent, notably lemons and many limes.
Citrus taxonomy
The trifoliate orange is a cold hardy plant distinguishable by its compound leaves with three leaflets and its deciduous nature, but is close enough to the genus "Citrus" to be used as a rootstock. Swingle moved the trifoliate orange from "Citrus" to its own genus, "Poncirus". It was long thought to be the only member of this genus, until a second species, "Poncirus polyandra", was discovered in Yunnan (China) in the 1980s. Early phylogenetic analysis nested "Poncirus" within the citrus, suggesting they all belong to a single genus, but the genomic sequencing of Wu, "et al.", placed it outside the cluster representing "Citrus", and the authors retained a separate "Poncirus" genus.