Native to Thailand, kaffir lime trees, small and shrubby, produce both a fruit and leaves, which can be used for culinary purposes. There are other species that just produce the fruit in Mexico, Tahiti and the West Indies but this is not the same and should not be confused. The leaves are the richest part of the plant and it is no wonder as the essential oils in the leaves and citral content is what gives it the zesty lemon and floral headiness in flavour and aroma.