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 lemon plant originates in Burma, where it is found growing wild: from there it crossed the Middle East, Mesopotamia, and Palestine, to the Mediterranean, where it found favorable conditions to thrive. The natural habitat of the lemon lies in a strip from the 40° parallel in the North to the 40° parallel in the South: this strip includes California, Uruguay, Argentina, South Africa and the Mediterranean basin, in particular Italy, Spain, Greece and Turkey. In the Fifteenth and Sixteenth centuries, when there was an aristocratic monopoly on citrus growing, the use of lemons was confined to luxury foods.