Citrus × limon ponterosa
At the NY Arboretum. The tree is very hardy and can handle frosts; the fruit are thick-skinned and very large. Likely a citron-lemon hybrid.
The exact origin of the lemon has remained a mystery, though it is widely presumed that lemons first grew in India, northern Burma, and China. In South and South East Asia, it was known for its antiseptic properties and it was used as an antidote for various poisons. Lemons entered Europe (near southern Italy) no later than the 1st century AD, during the time of Ancient Rome. However, they were not widely cultivated. It was later introduced to Persia and then to Iraq and Egypt around AD 700. The lemon was first recorded in literature in a 10th century Arabic treatise on farming, and was also used as an ornamental plant in early Islamic gardens. It was distributed widely throughout the Arab world and the Mediterranean region between AD 1000 and AD 1150. The genetic origin of the lemon, however, was reported to be hybrid between sour orange and citron. The first substantial lemon cultivation in Europe began in Genoa in the middle of the 15th century. It was later introduced to the Americas in 1493 when Christopher Columbus brought lemon seeds to Hispaniola along his voyages. Spanish conquest throughout the New World helped spread lemon seeds. It was mainly used as ornament and medicine. In the 18th and 19th centuries, lemons were increasingly planted in Florida and California, when lemons began to be used in cooking and flavoring.