Rhobs el Arsa
The Rhobs al Arsa has long been viewed as a citron hybrid, though a different cultivars have been suggested for the parent, for example, Moroccan citron as a male parent and sour orange as the female parent, citron or lemon and a mandarin., or citron and the lime. Detailed genomic analysis has shown Rhobs al Arsa to be highly similar to several cultivars of "Citrus limetta", the limetta or Persian sweet lime, and likely shared a common origin with them, arising from a cross between citron ("Citrus medica") and sour orange ("Citrus" × "aurantium"). The common lemon arose from a distinct hybridization event involving the same two species.
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.