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. It is found wild occasionally with its parent species.
It was first described by Linnaeus from specimens collected in England; he treated it as a species, but it is now universally agreed to be a hybrid.
It is a herbaceous rhizomatous perennial plant growing to tall, with smooth stems, square in cross section. The rhizomes are wide-spreading, fleshy, and bare fibrous roots. The leaves are from long and 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, long, with a four-lobed corolla about 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.
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.
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. Inhaling the vapor from peppermint oil or peppermint tea is said to reduce congestion. 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.
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, 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.
Outside of its native range, areas where peppermint was formerly grown for oil often have an abundance of feral plants, and it is considered invasive in Australia, the Galápagos Islands, New Zealand, and in the United States.
In the United States, Washington ranks number one in production of Peppermint Oil.
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.