Some of the many varieties of mint made clear.
Commercial Cultivation of peppermint and spearmint dates from 1750 in England; by 1790 the industry had migrated to the United States. Peppermint (Mentha x piperita) is primarily grown today in the fertile, sandy loam soils of the Pacific Northwest; “native” spearmint (M. spicata) and Scotch spearmint (M. x gracilis), in the muck soils of Michigan, Indianan, and Wisconsin. Most mint species are European natives that have naturalized elsewhere.
Spearmint and peppermint are grown primarily for their essential oil, which is enhanced by nitrogenous fertilizers and is at its maximum at the time of maximum bloom. Because the plants require long days (10 to 14 hours of light) to flower, large-scale mint production in the United States generally takes place north of the 40th parallel.
Of the 18 “pure” mint species mentioned below, the most economically important are M. spicata, M. aquatic, M. arvensis, M. suaveolens, and M. longifolia. These five extremely variable species are also the focus of most of the taxonomic confusion that surrounds mints. The primary distinguishing characteristics of mints are their odors, so the study of mint taxonomy deals mainly with the chemistry of their essential oils.
Because of the variation and extensive hybridization among mints, most are seed-sterile or do not come true from seeds. However, the abundant long, thin rhizomes, called stolons, offset any need for seed production. Mints are like stray cats: you take them in, give them some food, and they are yours forever.
The “Pure” Mints
M. spicata, spearmint, is named for its spiked inflorescence.
It is native to Europe but commonly naturalized around the world. This is a very variable species, including forms with leaves that are smooth, hairy, crisped, or wrinkled. The hairy forms, sometimes called silver mint, are often confused with M. longifolia, horsemint, but the odor of spearmint is definitive. The wrinkled form, sometimes called M. cordifolia or ‘Kentucky Colonel’, is naturalized throughout Central America, the American Southwest, and the Philippines.
M. arvensis, the European corn mint or field mint, is commonly cultivated in two forms: a green-leaved clone called ginger mint, previously designated as M. gentilis, and a virally infected clone called golden apple mint.
The latter is splashed with translucent yellow on leaves which develop in cool weather. Ginger mint has a lavender-like odor with strong fruity overtones. M. candadensis, the North American corn mint or field mint, was until recently considered a variety of M. arvensis, but now appears to be a separate species which includes the Eastern Asian corn mint of field mint, known in English as Japanese peppermint. Pennyroyal and peppermint scents predominate.
M. suaveolens, pineapple mint, was originally named from a variegated form.
The green form is sometimes called apple mint. The scent of these mints is musty, fruity, and pineapple-like; the literature also reports spearmint- and pennyroyal-scented forms.
M. longifolia, horsemint, is the name often assigned to hairy forms of spearmint. However, true horsemint is native to mountainous sections of Europe, Asia, and Africa, and is not naturalized in North America.
M. requienii, Corsican mint, is named after the French botanist and explorer M. Esprit Requien.
It has tiny leaves and even tinier flowers, and is characterized by a penny-royal-peppermint odor.
M. pulegium, pennyroyal, derives its name from the Latin pulex, meaning flea, alluding to its use as a strewing herb in European castles to repel fleas.
The definitive pennyroyal scent is derived from pulegone in the essential oil of this and other plants; true pennyroyal also has peppermint undertones. M. micrantha, M. gattefossei, and M. cervina are other mints with pennyroyal scent.
Section Australasica consists of eight species. M. satureioides, M. repens, M. diemenica, M. australis, M. grandiflora, and M. laxiflora are restricted to Australia and require cool summers and milk winters. M. cunninghamii has similar requirements and is endemic to New Zealand. M. japonica is native to Japan but does reasonably well in Calfornia.
Peppermint: A Special Case
Peppermint, M. x piperita, is native to Europe but commonly naturalized in North America. It is a sterile hybrid of spearmint (M. spicata) with water mint (M. aquatic). Because spearmint and water mint are quite variable, this seed-sterile hybrid is also variable. Known forms have leaves that may be smooth of crisped, green and/or purple or variegated. The three commonly cultivated forms are black or ‘Mitcham’ peppermint (M. x p. var. piperita), white peppermint (M. x p. var. officinalis), and crisped peppermint (M. x p. ‘Crispa’). Only the ‘Mitcham’ peppermint has achieved economic importance.
The flower heads and leaves of white peppermint resemble those of spearmint, and those of black peppermint resemble those of water mint. White peppermint lacks the dark purple to black color on the stems and leaves found in black peppermint. ‘Crispa’ peppermint inherited the odor of the spearmint parent, and is often mistakenly identified as a selection of M. acuatica. Grapefruit mint is a hairy and crisped form of peppermint.
The name “chocolate mint” has been applied in the United States to both black and white peppermints. “Blue balsam” and “candy” mints, some of the more common of this types, are variants of ‘Mitcham’, but in my opinion, they don’t really differ enough, in odor or otherwise, to warrant a separate name. Clones offered as chocolate mint differ little from peppermint forms that have been cultivated for more than 300 years.
Arthur O. Tucker, a professor emeritus of botany at Delaware State College in Dover, Delaware, looks at plants more closely and in more ways than most people can imagine.
For more about mint, here’s an excellent article from Mother Earth Gardner: Freshly Minted.
Or this special edition magazine all about unusual herbs: Mother Earth News Guide to Unusual Herbs.