Citrus limonum. Cultivated primarily in the Mediterranean basin, lemon originated in India. Its colour, sweet-to-sour ratios, scent and taste as well as abundance vary from species to species and from climate to climate. The maturity of the lemon tree and its growing region, or terroir, will also determine how prolifically it can provide essential oil and in how wide a diversity of flavours. Such qualities, along with a fruity, delicate scent, make lemon ideal for fighting off colds and flu.