Easily confused with : Horse Mint.

Hybridises with :

• Water Mint (Mentha aquatica) to produce Whorled Mint (Mentha × verticillata)
• Corn Mint (Mentha arvensis) to produce Bushy Mint (Mentha × gracilis)

Some similarities to other mints.

MONOTERPENE KETONES The chemical, Carvone, a typical terpene, is the main active ingredient (67 - 80%) in oil of spearmint) prepared by distillation of the leaves from Spear Mint. It is used in chewing gum and some toothpastes (other toothpastes might use oil of peppermint, or menthol). Pulgenone is used as a flavouring agent, its mild toxicity being of no concern at the low concentrations required, being less than 1/10,000th of the toxic dose. In the body it is metabolized to Menthofuran, shown below, which is 10 times as toxic as Pulgenone, but still of no safety concern. Pulgenone occurs in greater concentration in Pennyroyal, and has been implicated in human Pennyroyal poisoning in those un-able to metabolize Pulgenone into Menthofuran. The only difference between Pulgenone and Menthol below is the C=C double bond in Pulgenone which is a single bond in Menthone. Menthone is another, but minor, constituent of Spearmint, Peppermint and Pelargonium geraniums. Although it can exist in four different stereoisometric configurations, it is the (2S, 5R)-trans- enantiomer that is the most frequent in nature. Structurally, it is related to Menthol, and has a similar minty and aromatic smell and finds use in perfumes. The essential oil also contains 13-20% Limonene, 7% Eucalyptol, 2% Pulgenone (the main constituent of Pennyroyal) and 0.2% Menthone. It also contains Pinene (α-), Pinene (β-), Camphene, Carvacrol, Eugenol, Furfural, Ionone (β-), Menthofuran, Caryophyllene, Jasmone and many other minor constituents.

Further aromatic compounds found in Spearmint oil Menthofuran is also used as a flavouring agent, its toxicity being of no concern at the low concentrations required, being less than 1/1000th of the toxic dose. Menthofuran in higher concentrations can damage the liver, it is hepatotoxic, and high consumption of Pennyroyal can be harmful, especially to women. Ionones such as β-Ionone are so-called Rose Ketones so named because they are found in essential oils of Roses, as well as in the essential oils of some other plants. [Rose ketones not found within Spearmint include α-Ionone, γ-Ionone, β-Damascone, β-Damascenone, all of which smell fragrantly (in slightly differing ways) of rose petals and all are used in perfumery]. The Carotenes α-carotene, β-carotene, γ-carotene, xanthophyll and β-Cryptoxanthin all contain at one or both ends a molecule of β-Ionone. Indeed, β-Ionone is a degradation product of the Carotenoids α-carotene, βcarotene, γ-carotene and from the Xanthophyll-β-cryptoxanthin. Because β-Ionone can be converted to Retinol within the stomach of animals, all these carotenoids possess Vitamin A activity. But not all carotenoids have a molecule of β-Ionone at one or both ends, and cannot therefore all be converted into Retinol nor into Retinal, and therefore not all carotenoids exhibit Vitamin A activity. Jasmone is another aldehyde more typically found in Jasmine flowers, but also present in Spearmint. It has the fragrance of Jasmine and is used in perfumes. It exists in two isomers, cis- and trans-Jasmone, both smell similarly and is produced in plants from the Jasmonates such as Jasmonic Acid and Methyl Jasmonate which are a group of plant hormones. Jasmone can act as a pheromone to various insects, either as an attractant or a repellent. In plants Jasmone is derived from Linolenic acid. Furfural is a toxic aldehyde with the odour of almonds but is in no way related to another much more toxic chemical that also smells of (bitter) almonds: Hydrocyanic Acid. It is occasionally used in perfume. On exposure to air it turns yellow. It is manufactured commercially from Oat hulls but can also be obtained using a chemical process from other brans, corn cobs and from sawdust. It is an irritant to the skin and chronic exposure to the substance can lead to skin allergy and hyper-susceptibility to sunburn. It occurs in many foods but usually at sub-toxic concentrations. Compare Furfural with Tulipalin A.

It is Spearmint rather than Peppermint (Water Mint) which flavours the World famous Kendal Mint Cake.