LAMIACEAE – The Mint Family

by Adriana Lopez-Villalobos and Amelie Mahrt-Smith

Fans of alternative medicine are likely familiar with the mint family, the Lamiaceae. Many of these plants produce essential oils used to battle ailments or boost the immune system – for example, oil of oregano is a common herbal treatment for sore throats, and peppermint oil has a cooling effect that can alleviate sore muscles. Lamiaceae plants are also widely used to add flavour to dishes and drinks, such as sage and rosemary – both in the genus Salvia. Among the other curious properties of the plants in this genus, Salvia divinorium (sometimes known as sage of the diviners or simply Salvia) is psychoactive and is recreationally smoked, chewed or consumed as a tea to induce hallucinations.

There are a variety of chemical compounds responsible for the different properties of plants in the Lamiaceae family. Within the Nepetoidae subfamily, which contains many of the more familiar Lamiaceae plants, the phenolic compound rosmarinic acid is mainly responsible. It was named after the plant from which it was first isolated, Salvia rosmarinus, also known as rosemary. This acid has shown antiviral, antimicrobial, and antioxidant activities. It has also been reported to deter pests like the tobacco hornworm (Manduca sexta).(4) Plants containing rosmarinic acid are most used to treat inflammation – and advances in molecular genetics help to explain why they are effective. In basic terms, rosmarinic acid stops the production of compounds that initiate inflammatory responses when cells are under stress – for example, from a viral infection. The acid inhibits the genes that tell the cell to make inflammation-inducing compounds and thus eases the symptom.(2)

Unsurprisingly, the Lamiaceae have been used in traditional medicine around the world for generations. The common characteristics of this family may have helped early peoples to recognize that a variety of different species can be used for food and medicine – the resemblance between species is strong, especially as you move from the family to the subfamily or to the genus level. Plants in the mint family usually have simple leaves, and they are always oppositely arranged. The stems are usually four-angled, with the leaves at each node being rotated 90° so that the leaves grow in four directions away from the stem. The flowers, which can be hermaphrodite or functionally female (i.e. The male parts are sterile), usually have five lobes and two ‘lips’ – hence the synonym Labiatae which is sometimes used to describe this family. The plant itself often has dense glands and a strong aroma.(3) Using these characteristics, you can identify common plants in the mint family that may be growing around your neighbourhood!

Glechoma hederacea – Ground Ivy

A native to Europe, G. hederacea is a creeping herb that was brought over deliberately by settlers for medicinal use and food and it quickly invaded the North American lands. It is low to the ground and inconspicuous – it can be recognized by its oppositely arranged, kidney-shaped leaves with blunt teeth, and blue-violet flowers about ½ inches long. It flowers in late spring and early summer, and by this time of year has already set seed. The upper lip of the corolla has three lobes that appear to be three distinct petals; the lower lip has two lobes with spots that are usually purple but occasionally pink or white. It flowers early in spring, and by mid-summer has produced seeds. However, it spreads much more rapidly by producing clones than seed dispersal. It is also suspected to have allelopathic effects, which helps it outcompete other plants and rapidly take over an area.(1)

Glechoma hederacea is a member of the Nepetoideae subfamily, so the presence of rosmarinic acid and other chemical compounds makes it a good contender for medicinal use. It is an effective anti-inflammatory agent and as such has been used against catarrh, the excess buildup of mucus caused by inflammation of the body’s mucus membranes.

Prunella vulgaris – Self-heal

Named for its ubiquitous use in traditional medicine, the selfheal is a Holarctic species – native to the continents of the northern hemisphere. It is also a member of the Nepetoideae subfamily and contains rosmarinic acid as the major phenolic compound. It has been said to treat sore throats, fevers, and accelerate wound healing.(5) Prunella vulgaris has also been shown to have specific activity against herpes simplex virus (HSV). Chemical compounds produced by the plant are shown to be effective at reducing the viral load of cells infected with HSV and has the potential to be used as an antiviral treatment for cold sores.(6)

The leaves are lance-shaped and entire, arranged oppositely as is typical of the Lamiaceae. The flowers are violet or purple and found in short spikes. It flowers from late spring to fall and can be found along roadsides and in waste places throughout Kingston, ON right now!

Because of the widespread medicinal and culinary uses of plants in the Lamiaceae family, European colonists brought many of them around the world with them. In addition to intentional introductions, seeds and fragments of plants can hitchhike along with other biological materials brought by settlers. For example, Lamium amplexicaule, also known as common dead-nettle is one of many members of the Mint family that was introduced to North America from the Old World. This specimen was collected in Kingston by George Lawson in 1859. Lawson was appointed professor of Chemistry and Natural History at Queen’s University in 1858, where he set up a botanical laboratory. He was also a founding member the Botanical Society of Canada, established in 1860. His wife, Mrs. Lawson, was an amateur botanist, and inspired equal privileges for female members of the Society. He was an ambitious man and saw the Botanical Society as a means of encouraging botanical research beyond the British settlements in Canada.(7) Although he only stayed a few years at Queen’s before moving on to Dalhousie University, his legacy remains at Queen’s in the specimens that are kept within the Fowler Herbarium.

References

  1. Hutchings, M. J., and E. A. C. Price. 1999. Glechoma hederacea L. (Nepta Glechoma Benth., N. hederacea (L.) Trev.). Journal of Ecology 87:347 – 364.
  2. Kim, J., S. Song, I. Lee, Y. Kim, I. Yoo, I. Ryoo, and K. Bae. 2011. Anti-inflammatory activity of constituents from Glechoma hederacea var. longituba. Bioorganic & Medicinal Chemistry Letters 21:3484 – 3487.
  3. Kokkini, S., R. Karousou, and E. Hanlidou. 2003. Herbs of the Labiatae. Pages 3082 – 3090 in L. Trugo, and P. M. Finglas, editors. Encyclopedia of Food Sciences and Nutrition (Second Edition). Academic Press.
  4. Petersen, M., and M. S. J. Simmonds. 2003. Rosmarinic acid. Phytochemistry 62:347 – 364.
  5. Psotoyá, J., M. Kolář, J. Soušek, Z. Švagera, J. Vičar, and J. Ulrichová. 2003. Biological activities of Prunella vulgaris. Phytotherapy Research 17:1082 – 1087.
  6. Xu, H., S. H. S. Lee, S. F. Lee, R. L. White, and J. Blay. 1999. Isolation and characterization of an anti-HSV polysaccharide from Prunella vulgaris. Antiviral Research 44: 43 – 54.
  7. Zeller, S. Lawson, George. 2003. In Dictionary of Canadian Biography, vol. 12, University of Toronto/Université Laval,– accessed online on July 20th, 2020.  http://www.biographi.ca/en/bio/lawson_george_12E.html.

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