Mint is one of the oldest known herbs. It even figures in Greek Mythology. According to myth, there was a nymph named Mentha (the genus name for mint today), who angered Pluto’s wife, Persephone. She was so angry that she turned Mentha into this aromatic herb we call mint. There are between 25 and 30 different species of mint. These have been hybridized into over six hundred different varieties. But of all of these, there are only two that we like best. They are peppermint, spicy and more pungent with green leaves and a peppery flavor, and spearmint, with a milder flavor and fragrance and gray-green or true green leaves. Mint has many relatives. Probably as much as a third or more of our modern culinary herbs are related to the mint family. Herbs like basil, marjoram, oregano, rosemary, and savory to name a few.
Culinarily speaking, when a recipe is sweet, i.e. a dessert, and it just calls for mint, it is understood that it should be peppermint. On the other hand, if the recipe is savory and calls for mint, it is understood that is should be spearmint. Mint leaves are used in teas, beverages, jellies, syrups, candies, and ice creams. In both Middle Eastern and British cuisines mint is used on lamb dishes. As a good Kentucky Colonel, I must also point out that you must have mint to make the official drink of the Kentucky Derby, the Mint Julep. This drink calls for spearmint, which is muddled (crushed by a wooden implement that resembles a small baseball bat). A similar approach is used for a Mojito. Then there is Crème de Menthe, a mint flavored liqueur (made from Corsican mint) used to make drinks like Grasshoppers.
Mint is usually the flavor that is used when the pharmaceutical and medical industry are trying to get us to take something that may not taste too good by itself. It is found in a lot of dental products like tooth pastes and mouth washes. Since mint grows wild worldwide, there should be no need for substitutions.