Mentha — the mints — is a genus of aromatic, mostly perennial herbs in the mint family (Lamiaceae), instantly recognizable for its square branching stems, opposite leaves, and pungent menthol-tinged fragrance. Plants typically grow between 10 and 120 cm tall, spreading aggressively underground by stolons and rhizomes that send up new shoots wherever conditions are damp enough to support them. The leaves are oblong to lanceolate with serrated margins, often softly downy, and range in color from deep green and gray-green through purple, blue-tinged and occasionally pale yellow in cultivated forms.
The flowers are small but produced in dense, showy false whorls called verticillasters, stacked along the stem or gathered into terminal spikes. Each flower has a two-lipped corolla — white through pale lilac to deeper purple — with four stamens and a four-lobed corolla in which the upper lobe is formed from two fused petals. Pollinated flowers ripen into clusters of nutlets, each containing one to four tiny seeds, though seed-grown plants are notoriously variable and most cultivated mints are propagated vegetatively to keep their flavor true.
Mentha is one of the most taxonomically tangled genera in horticulture. Plants of the World Online currently accepts about 26 species, while other treatments list anywhere from 18 to 25, and SEINet describes the group as roughly 25 species mainly distributed across Eurasia and Australia with one circumboreal taxon. More than three thousand names have been published in the genus over the centuries, most of them synonyms or illegitimate, the result of rampant hybridization, polyploidy and chromosomal reshuffling that has produced an enormous swarm of intermediate forms. Several of the most familiar culinary mints — peppermint (Mentha × piperita) chief among them — are stabilized hybrids rather than pure species, which is why so many garden mints refuse to come true from seed.
The genus is essentially cosmopolitan, native to a vast belt across Europe, temperate Asia, Africa, North America and Australasia, and naturalized far beyond that through centuries of cultivation. Almost all mints favor moist to wet ground: streamsides, ditches, lake margins, damp meadows and partially shaded woodland edges. That preference, combined with their rhizomatous habit, makes them prolific colonizers wherever they escape cultivation, which is why mint is so often grown in sunken pots or bottomless containers to keep its runners in check.
Mentha's economic and cultural footprint is huge. Menthol — making up 40 to 90 percent of essential oil in some species — is the active aromatic behind peppermint and spearmint flavorings used in confectionery, toothpaste, chewing gum, liqueurs, cocktails such as the mojito and mint julep, and traditional preparations such as Maghrebi (Touareg) tea, British mint sauce, and South Asian mint chutneys. Medicinally, mints have been used since antiquity for digestive complaints, headaches and oral hygiene, and peppermint oil has preliminary clinical support for irritable bowel syndrome. Mint oil also works as a low-toxicity insect repellent against ants, wasps and cockroaches.
Etymology
The genus name Mentha comes directly from Latin mentha (also spelled menta), itself borrowed from Greek mintha, minthē or mintē, meaning spearmint. In Greek mythology the plant was identified with the nymph Minthe, a lover of Hades who, according to the story, was transformed into the fragrant herb. The same root carries through to English "mint" and to cognate words across the Romance and Germanic languages.
Distribution
Mentha has what botanists call a subcosmopolitan distribution: native populations stretch across Europe, temperate and subtropical Asia, parts of Africa, much of North America, and Australasia, with Plants of the World Online listing more than 200 native regions ranging alphabetically from Afghanistan to Zimbabwe. Beyond its native range the genus has been carried by gardeners, herbalists and accidental introductions to virtually every habitable continent; POWO records it as introduced in Hawaii, the Juan Fernández Islands, the Society Islands, Uruguay and Venezuela, among others, and SEINet notes that many Eurasian species have naturalized widely in North America after escaping cultivation. National floras such as Switzerland's Info Flora catalogue both wild species (M. aquatica, M. arvensis, M. longifolia, M. pulegium, M. spicata, M. suaveolens) and the common hybrids (M. ×piperita, M. ×verticillata, M. ×villosa) that thrive alongside them.
Ecology
Mints are creatures of damp ground. Most species are happiest along the edges of streams, ponds, ditches and seasonally wet meadows, or in cool moist soils in partial shade — a preference that explains both their patchy distribution in arid regions and their tenacity in irrigated gardens. The genus's reproductive ecology is dominated by hybridization: where two or more species' ranges overlap, polyploidy and chromosomal rearrangement repeatedly throw up stabilized intermediate populations that establish themselves in the wild, so the boundary between "species" and "naturalized hybrid swarm" is unusually blurred in Mentha. Mints support a range of insect herbivores too — buff ermine moth larvae and other Lepidoptera feed on the foliage, and specialist beetles such as the blue mint beetle are reliable visitors to garden plantings.
Cultivation
All mints thrive in cool, moist conditions near water — pond margins, damp borders, partially shaded beds — and tolerate a wide range of soil types so long as they don't dry out. Most cultivated species are hardy across roughly USDA zones 5 to 9. The genus's signature challenge in the garden is containment: mints spread aggressively through underground runners, so gardeners commonly grow them in deep bottomless containers sunk in the soil, or in above-ground pots, to prevent them from overtaking neighboring plantings. Because so many garden mints are hybrids, vegetative propagation by cuttings or division of rhizomes is the only reliable way to preserve a particular flavor or leaf color.
Propagation
Mentha is propagated almost exclusively by vegetative means. Cuttings and division of rhizomes are preferred because seed-grown plants are notoriously variable and the popular hybrid mints — peppermint and the apple-mint hybrids in particular — do not come true from seed at all. A short stem cutting taken in the growing season roots readily in damp soil or even a glass of water, and a fragment of rhizome lifted from an established clump will quickly establish in a new spot.
Cultural Uses
Few plants have a longer cultural résumé than mint. In the kitchen, fresh and dried leaves flavor teas, syrups, candies, ice creams, jellies and savory sauces; mint is essential to British mint sauce served with lamb, to Indian curries and chutneys, to Middle Eastern lamb dishes, to Maghrebi Touareg tea, and to classic cocktails such as the mojito and the mint julep. Industrially, menthol — which makes up 40 to 90 percent of the essential oil in some Mentha species — is one of the world's most heavily produced flavor and fragrance compounds, used in toothpaste, chewing gum, confectionery, cosmetics, perfumes and aromatherapy. Medicinally the genus has been used since antiquity for stomach upsets, headaches and oral hygiene; peppermint preparations have preliminary clinical support for irritable bowel syndrome and post-surgical nausea, though large doses of essential oil can be toxic and have historically been associated with abortifacient effects. Mint oil also serves as an environmentally friendly insecticide effective against wasps, hornets, ants and cockroaches, and the dried herb was once strewn across European floors as a deodorizer.
History
Mentha has a deep paleontological and cultural record. Fossil seeds of an extinct species, Mentha pliocenica, have been recovered from Pliocene deposits in Belarus, where they closely resemble the seeds of modern M. aquatica and M. arvensis, suggesting the genus has been part of European wetlands for millions of years. Human use is equally long-standing: ancient Greeks rubbed mint on their arms in the belief that it increased physical strength, and through the Middle Ages and into the early modern period mint was strewn across European floors as a household deodorizer so that its scent would be released underfoot.
Taxonomy Notes
Mentha L. was published by Linnaeus in Species Plantarum in 1753 and sits in family Lamiaceae, subfamily Nepetoideae, tribe Mentheae, order Lamiales. Mentha spicata is the type species. Estimates of species number vary considerably across authorities: Plants of the World Online currently accepts 26 species, SEINet's treatment recognizes about 25, and Wikipedia cites estimates of 18 to 24 — a spread that reflects how hard the genus is to circumscribe. More than 3,000 names have been published in Mentha, most of them synonyms or illegitimate, because hybridization, polyploidy and chromosomal aberration have generated an enormous number of intermediate populations that have at various times been described as distinct species. GBIF records 493 species- and subspecies-rank descendants under the genus, the great majority of which are synonyms.
