Mentha × piperita

Peppermint (Mentha × piperita) is a hybrid mint, a cross between watermint (Mentha aquatica) and spearmint (Mentha spicata). The plant is indigenous in Europe and now widespread in cultivation throughout all regions of the world^[1]. It is found wild occasionally with its parent species.^[1]^[2]

Botany

It was first described by Linnaeus from specimens collected in England; he treated it as a species,^[3] but it is now universally agreed to be a hybrid.^[4]

It is a herbaceous rhizomatous perennial plant growing to 30–90 cm (12–35 in) tall, with smooth stems, square in cross section. The rhizomes are wide-spreading, fleshy, and bare fibrous roots. The leaves are from 4–9 cm (1.6–3.5 in) long and 1.5–4 cm (0.59–1.6 in) cm broad, dark green with reddish veins, and with an acute apex and coarsely toothed margins. The leaves and stems are usually slightly hairy. The flowers are purple, 6–8 mm (0.24–0.31 in) long, with a four-lobed corolla about 5 mm (0.20 in) diameter; they are produced in whorls (verticillasters) around the stem, forming thick, blunt spikes. Flowering is from mid to late summer. The chromosome number is variable, with 2n counts of 66, 72, 84, and 120 recorded.^[2]^[5]^[6]

Ecology

It typically occurs in moist habitats, including streamsides and drainage ditches. It is usually sterile, producing no seeds and reproducing only vegetatively, spreading by its rhizomes.^[2]^[5]

Uses

Peppermint is sometimes regarded as 'the world's oldest medicine', with archaeological evidence placing its use at least as far back as ten thousand years ago.^{citation needed}

Peppermint has a high menthol content, and is often used as a flavouring in tea, ice cream, confectionery, chewing gum, and toothpaste. The oil also contains menthone and menthyl esters. It is the oldest and most popular flavour of mint-flavoured confectionery. Peppermint can also be found in some shampoos and soaps, which give the hair a minty scent and produce a cooling sensation on the skin.

Peppermint, like many spices and herbs, is believed to have medicinal properties when consumed. It is said that it helps against upset stomachs, inhibits the growth of certain bacteria, and can help soothe and relax muscles when inhaled or applied to the skin. Other health benefits are attributed to the high manganese, vitamin C and vitamin A content; as well as trace amounts of various other nutrients such as fibre, iron, calcium, folate, potassium, tryptophan, magnesium, omega-3 fatty acids, riboflavin, and copper.

In 2007, Italian investigators reported that 75% of the patients in their study who took peppermint oil capsules for four weeks had a major reduction in irritable bowel syndrome (IBS) symptoms, compared with just 38% of those who took a placebo pill.^[7]

Similarly, some poorly designed earlier trials found that peppermint oil has the ability to reduce colicky abdominal pain due to IBS with an NNT (number needed to treat) around 3.1,^[8] but the oil is an irritant to the stomach in the quantity required and therefore needs wrapping for delayed release in the intestine. Peppermint relaxes the gastro-esophageal sphincter, thus promoting belching.

Peppermint flowers are large nectar producers and honey bees as well as other nectar harvesting organisms forage them heavily. A mild, pleasant varietal honey can be produced if there is a sufficient area of plants.

Peppermint oil is used by commercial pesticide applicators, in the EcoSmart Technologies line of products, as a natural insecticide.^{citation needed}^[9]

In the United States, Washington ranks number one in production of Peppermint Oil.^[12]

Cultivation

Peppermint generally thrives in shade and expands quickly by underground rhizomes. If you choose to grow peppermint, it is advisable to plant it in a container, otherwise it can rapidly take over a whole garden. It needs a good water supply, and is ideal for planting in part-sun to shade areas.

The leaves and flowering tops are the usable portion of the plant. They are collected as soon as the flowers begin to open and then are carefully dried. The wild form of the plant is less suitable for this purpose, with cultivated plants having been selected for more and better oil content. Seeds sold at stores labelled peppermint generally will not germinate into true peppermint, but into a particularly poor-scented spearmint plant. The true peppermint might rarely produce seeds, but only by fertilisation from a spearmint plant, and contribute only their own spearmint genes.

Cultivars

References

^ ^a ^b Euro+Med Plantbase Project: Mentha × piperita
^ ^a ^b ^c Flora of NW Europe: Mentha × piperita
^ Linnaeus, C. (1753). Species Plantarum 2: 576–577.
^ Harley, R. M. (1975). Mentha L. In: Stace, C. A., ed. Hybridization and the flora of the British Isles page 387.
^ ^a ^b Blamey, M. & Grey-Wilson, C. (1989). Flora of Britain and Northern Europe. ISBN 0-340-40170-2
^ ^a ^b Huxley, A., ed. (1992). New RHS Dictionary of Gardening. Macmillan ISBN 0-333-47494-5.
^ Cappello, G.; et al. (2007). "Peppermint oil (Mintoil®) in the treatment of irritable bowel syndrome: A prospective double blind placebo-controlled randomized trial". Digestive and Liver Disease 39 (6): 530–536. doi:10.1016/j.dld.2007.02.006.
^ Bandolier Journal: Peppermint oil for irritable bowel syndrome
^ EcoSMART Product label
^ Pacific Island Ecosystems at Risk: Mentha x piperita
^ USDA Plants Profile: Mentha x piperita
^ State of Washington: Washington's Rank in the Nation's Agriculture
^ Mountain Valley Growers: Mentha piperita cv. Chocolate Mint

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