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.
Moroccan citron
Chapot was probably first to describe this variety of citron in detail, along with illustrations of many forms of the fruit, and all the properties of the shrub, leaves and blossoms. He also mentions that the true citron of Morocco, which is traditionally only grown in the region of Assads, for the sake of the mitzva of four species, and is oblong, acidless and rather dry, is much different than the rounded citron hybrid, Rhobs el Arsa, that is more commonly grown for food in the entire country of Morocco, and its taste is acidic and fruity.