Ponderosa lemon
The ponderosa lemon originated in roughly 1887, and is believed to come from a chance seedling grown in Hagerstown, Maryland. It was later named and introduced to the nursery trade in 1900. Though often referred to as a cross between the lemon and citron, a recent genomic analysis showed it to solely contain pomelo ("Citrus maxima") and citron ("Citrus medica") DNA, perhaps being an F2 hybrid. Thus they cannot derive from true lemons, which have a mandarin orange component.
Siracusa Lemon
The Siracusa lemon (in Italian, "Limone di Siracusa IGP") is the fruit of the cultivar "femminello siracusa" and its clones, corresponding to the botanical species Citrus x limon L. Burm. The "femminello siracusano" cultivar is the most common variety of lemon in Italy, with the Province of Syracuse (Siracusa) region accounting for 42% of the national lemon-growing land area.