Peppermint (Mentha × piperita)
Peppermint (Mentha × piperita) is a sterile allohexaploid hybrid of three Mentha species: spearmint (M. spicata), which itself is a cross of M. longifolia and M. suaveolens, and watermint (M. aquatica). It is believed to have originated in Mitcham, England, in the 18th century or earlier, and has since spread around the world. Because of peppermint’s sterility, its reproduction occurs only through vegetative propagation by rhizomes and stolons. The name peppermint refers to the pungent taste of its essential oil, which is rich in monoterpenes, such as menthol and menthone. The composition and yields of this highly valuable oil depend on several environmental factors including day length, humidity, and night temperatures. In the United States, such favorable growth conditions are found in Washington, Oregon, and Idaho. Annual peppermint crops in these states exceed 2 million pounds.
Peppermint oil is produced and stored in peltate glandular trichomes on the aerial surfaces of the plant that are typical for species from the Nepetoidae subfamily of the Lamiaceae (mint) family. Isolated peppermint trichomes have served as a model system for detailed studies of terpene biosynthesis. The essential oil is retrieved from fresh plant material by steam distillation and predominantly used as flavoring agent for toothpastes, chewing gum, and candy. In addition, peppermint (both dried herb and oil) has a long tradition of medicinal application, primarily for gastrointestinal and biliary disorders, but also in the treatment of common cold symptoms, headaches, and skin irritations. Dried peppermint leaves are used for tea preparation, or as tincture component. In vitro, peppermint oil and its components have been shown to exert anti-oxidant and antimicrobial effects. In animal models, spasmolytic and chemopreventive activities have been demonstrated.