Not to be semantically confused with Spear-Leaved Orache (Atriplex prostrata), Spear Thistle (Cirsium vulgare),
Spear-leaved Willowherb (Epilobium lanceolatum), Greater Spearwort (Ranunculus lingua), Lesser Spearwort (Ranunculus flammula) or
Adder's-tongue Spearwort (Ranunculus ophioglossifolius) [plants from disparate families with similar names].
Hybridizes with :
Some similarities to other mints.
Spearmint can exist as two or more Chemotypes, where exactly the same species of plant can produce differing secondary metabolites, which might depend upon the region it is growing in or on environmental factors. This is why sometimes it instead does not smell of spearmint.
It is an Archaeophyte of the denizen type - meaning that it can compete with already established vegetation like a native plant usually does. It is widely grown then naturalised in waste or rough ground.
It is a tetraploid, meaning it has 4 sets of identical chromosomes and it is a product of the hybrid between
Horse Mint (Mentha longifolia) [which does not grow in the UK] and Round-Leaved Mint (Mentha Suaveolens) and can have characteristics almost anywhere between those two Mints.
Easily confused with :
Horse Mint (Mentha longifolia) (but that doesn't grow in the UK)...
It is used to produce the well-known spearmint taste/smell in sweets (which is due to the presence of
Carvone), such as Wriglys' Spearmints.
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).
Carvone exists in two different stereoisomers which smell completely different to each other. The first, (R)-Carvone is the one found in Spearmint and Corn Mint and smells of peppermint; whereas (S)-Carvone is found in
Caraway and smells accordingly.
With animals (and all other creatures) being constructed from chiral molecules, it is then perhaps no surprise that another chiral molecule (Carvone in this instance), smells completely differently depending upon which chiral form, (R)-Carvone, or (S)-Carvone, is presented to the smell sensors. This is not a unique occurrence; many molecules work completely differently in humans (and other creatures) depending on the exact stereoisometric form present. Sometimes one stereoisometric form will work as intended whilst the other form is toxic.
Pulgenone (not to be confused with Pulegone, which it resembles chemically, but the two are not identical) 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 α-Pinene, β-Pinene, Camphene, Carvacrol, Eugenol,
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,
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, β-Carotene,
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
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. Exists in two isomers, cis- and trans-Jasmone (both of which smell similarly) it 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
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.