Lemon

The lemon tree is a small thorny evergreen about 3 to 6 metres tall with white, purple-tinged, fragrant flowers. The oval yellow fruit has a thick aromatic peel and sharply sour juice, and each fruit holds several to a dozen or more seeds. The seeds are ovoid, plump or slightly flattened, 8 to 12 millimetres long, cream to pale tan with a pointed tip and a smooth, slippery coat. They are strongly bitter because of limonoids such as limonin. Seeds are removed before cooking, though a few are harmless. Some modern varieties are nearly seedless. Seeds are sold only for growing, and potted citrus is often raised from them as a houseplant.

The lemon is a hybrid between citron and sour orange, which arose in northeastern India, northern Myanmar or southern China. The earliest records of lemons come from Arab and Persian sources, and the fruit spread through the Islamic world to the Mediterranean in the first millennium. The English word lemon comes through Old French limon from Arabic laymun and Persian limu, ultimately from an Indian language source. Seeds of true lemons come true only in part, since lemons can produce several embryos in one seed, some of which clone the mother tree.

Lemons were grown in Italy by about the second century, but they became an important crop only after the Arab expansion, when they were planted in Spain and Sicily. Crusaders brought lemons back to northern Europe, and by the fifteenth century Genoa, Liguria and Amalfi were trading them. Christopher Columbus carried lemon seeds to Hispaniola in 1493, and Spanish settlers planted them across the Americas.

Lemons are famous in the history of medicine because sailors used citrus juice to prevent scurvy. The Scottish naval surgeon James Lind conducted a controlled trial in 1747 that suggested citrus fruits were effective, though the Royal Navy did not adopt them as standard issue until later, and limes were eventually used instead. California's lemon industry arose during the Gold Rush, as lemons were sold to miners.

The lemon seed has always been the means of propagation for new rootstocks in nurseries, and growers today use seedlings of hardy citrus as rootstock on which good varieties are grafted. The bitterness of the seed has meant it plays no part in cuisine, though some modern cooks use ground seeds sparingly for a bitter flavour.

Seeds are mainly used for growing: planted in warm, moist soil they sprout in a few weeks, giving glossy houseplants that rarely fruit well. Nurseries raise rootstock from them. In small amounts, pips are included in homemade pectin extractions because they contain pectin, and some cooks use ground seeds in bitter marinades, although this is unusual. Folk traditions use seed powder or tea for digestion, but this is not well studied. The juice, zest and peel are the primary culinary parts and are used in drinks, baking, preserves, cleaning products and perfumery.

Lemon juice is a source of vitamin C and flavonoids such as hesperidin and eriocitrin. Seeds contain limonoids, flavonoids and oils, and some laboratory studies suggest antioxidant and antimicrobial effects, but there are no sound human trials. Seeds are not an established food or supplement. Concentrated seed extract products are sold as health items, and their claims are mostly unproven. Normal use of the juice in food is considered healthy for most people.