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.
Greek citron
"This tree does not become particularly big. The leaves are smaller than those of other citrons, and serrated, oblong, pointed towards the front, mixed with many thorns. The bloom is small and reddish from outside. The fruit blossoms (- "the carpels") are not less oblong from the beginning, appearing as reddish and dark-green; thereafter they turn entirely green, and when they ripen, straw-yellow, remaining, however, rather small all the time and never growing to a proper size, like other kinds of Citron.