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.
Bitter orange
Bitter orange, Seville orange, sour orange, bigarade orange, or marmalade orange refers to a citrus tree (Citrus" × "aurantium) and its fruit. It is native to southeast Asia, and has been spread by humans to many parts of the world. Wild trees are found near small streams in generally secluded and wooded parts of Florida and The Bahamas after it was introduced to the area from Spain, where it had been introduced and cultivated heavily beginning in the 10th century by the Moors. The bitter orange is believed to be a cross between "Citrus maxima" × "Citrus reticulata"