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.
Citrus taxonomy
The pomelo ("Citrus maxima"), a second of the core species from which most citrus hybrids have derived, is native to southeast Asia. Among the hybrids deriving from mandarin/pomelo crosses, there is a direct correlation between the proportion of pomelo DNA in the hybrid and fruit size, while the more palatable mandarins are those that have received specific genes from pomelos that alter their acidity. Some of the more common pomelos are genetically pure, while a number have a single small region of introgressed mandarin DNA on one chromosome, the result of a cross followed by extensive backcrossing with pomelo.