The American Spice Trade Association defines the term "spices" very broadly as "the products of dried plants, essentially used for seasoning food." With the exception of saffron, these spices are cultivated in tropical or semitropical climates. In these products, only certain parts of the plant are used: the berries of allspice the fruit of cardamom, pepper, and vanilla; the rhizome of calamus, ginger, and curcuma; buds of cloves; stigma of saffron flowers; bark of cinnamon; seeds of nutmeg; and the aril of mace. Often essential oils are extracted from leaves. Curcuma, the least expensive and most widely used, is an excellent substitute for saffron. The essential oils and oleoresins of spices, like those of the principal aromatic herbs, have not revealed all their secrets. Oleoresin yields obtained after the removal of solvents are always higher than those of essential oils and largely depend on the type of solvent used.