Wintergreen

Common Name: Wintergreen, Teaberry, Checkerberry, Boxberry, Mountain tea, Deer berry, Ground holly, Spiceberry. Often confused with Partridgeberry due to similarities in ground hugging habitat, berry size, and color – In a forest of deciduous trees that is otherwise nearly denuded in winter, the clusters of bright green shiny leaves that cover the ground in large swaths are eye catching, a reminder that even in winter there is green ― wintergreen.

Scientific Name: Gaultheria procumbens – Jean François Gauthier was the royal physician and botanist for King Louis XV in the North American colony of New France. The Swedish/Finnish naturalist Peter Kalm, an apostle of Carl Linnaeus, honored Gauthier with the eponymous genus name in recognition of the support he had provided during Kalm’s expedition to North America in 1748. The species name is  from the Latin verb procumbere which means to fall, bend, or lean forward. Procumbent is a botanical term for plants that have stems that trail along the ground without putting down roots.  

Potpourri: Wintergreen is a contradiction in terms. Winter is white snow and occasionally black ice. In the waning light of autumn, leaves of deciduous trees turn from green to yellow and/or red and eventually brown as they die and fall to become a part of the earthworm-churned humus below. Trees with leaves or needles that don’t fall in fall are called evergreen as they always are (ever green); winter has nothing to do with it. The seasonal oxymoronic distinction for the diminutive ground cover is likely a matter of perspective. The expanse of shiny bright green leaves trailing through the woods is in stark contrast to the browns and grays of the wintering forest floor. Wintergreen is most notable for the aroma and flavor of its leaves and berries. The name wintergreen accordingly evokes the freshness of the mountain air in winter and is a metaphor for natural purity. Like all floral emanations, however, wintergreen is produced by the plant for its own purpose absent any human influence.

Wintergreen is a member of the heath family, Ericaceae, derived from ereike which is the Greek name for heather. The ericoids are predominantly perennial, woody shrubs and herbs that occupy acidic uplands with low soil fertility ― they necessarily evolved survival strategies suited to these distressed, niche areas. Among the roughly 2,000 heather-type plants are some of the most noteworthy montane species including mountain laurel, pink azalea or Pinxter flower, mountain rosebay or Catawba rhododendron, and high-bush blueberry. In many cases, heath plants dominate their habitat, crowding out the competition to create a virtual monoculture in the understory. This is evidenced by the dense stands of mountain laurel and rhododendron in the northern and southern Appalachians respectively.  Wintergreen is their diminutive cousin, consisting of leathery, alternate leaves with a distinctive sheen and almost imperceptible teeth along the margin. Bell-shaped flowers scented to attract pollinating bumblebees become the red berries of autumn that persist into winter. Red attracts foraging birds to consume the pulp, depositing the indigestible seeds remotely in a dollop of nutritious excrement. [1]

Wintergreen flowers attract pollinators

Marginal habitats are especially challenging for all living things. Animals have the option to rove in and out seasonally in search of food and surreptitiously to avoid predators. Plants and fungi are sessile, growing only upward and outward from a set datum. Once they establish underground interconnected networks of roots and mycelia (the” wood wide web”), the die is cast. Any and all interaction with the outside world to attract benefactors and repel invaders becomes a matter of plant physiology. Metabolism is the general name for the chemistry of growth and decay, consisting of both the new tissue growth of anabolism and the energy creation and waste disposal of catabolism. Plants produce hundreds of thousands of primary and secondary chemicals for metabolism called metabolites that are both necessary and sufficient for attraction and repulsion.  Metabolites with low molecular weight and an affinity for fat (lipophilic) are often volatile, becoming airborne due to evaporation when exposed to air at ambient temperature. The most effective way to communicate at a distance is to take advantage of atmospheric motion and dispersal. More than 7,000 volatile plant metabolites have been identified from foods and beverages. [2] The volatile oil that is produced by the wintergreen plant is methyl salicylate.

Methyl salicylate is a colorless liquid at room temperature and consists of 8 carbon, 8 hydrogen and 3 oxygen atoms with the formula (C8H8O3). [3] Fresh wintergreen leaves have less than 1 percent by dry weight (technically called weight percent abbreviated wt%). The oil is extracted by bulk fermentation of harvested leaves; an enzyme breaks the chemical bond to release almost pure (96-99 wt%) methyl salicylate. [4] Volatile oils like wintergreen probably originated due to the random mutation of evolution as a way to deter herbivores. While herbivore is generally applied to distinguish vegetation eating as an alternative to meat eating among animals, here it refers to leaf eating insects that were a primary threat to primordial plants. Methyl salicylate evolved independently of wintergreen in other plant species, as similar threats to survival yield similar reactions. This is a well-documented phenomenon called convergent evolution. Over the eons, the original volatile plant oils evolved further to promote survival, taking on a wide variety of functions such as attracting some animals and repelling others. The complex nature of plant chemical interactions with their environment remains largely opaque to science absent those subject to field study ― like methyl salicylate. [5]

Botanists have suspected of over half a century that there was one phytochemical (phyton means plant in Greek) responsible for triggering plant defensives in response to alien invaders. Defensive behavior had been observed by within an individual plant and remarkably from one plant to another ― presumably via volatile chemical communication. Salicylic acid was suspect for a time but testing of specific defensive response failed to correlate with concentrations of the chemical. Continued research revealed that SABP2, the enzyme that converts methyl salicylate to salicylic acid, is the probable intraspecies signal. The observed phenomenon is attributed to a plant producing methyl salicylate at the damaged site and transmitting it through its vascular system with SABP2 converting it to salicylic acid to trigger resistance remotely. [6] And that is not all. Methyl salicylates attract predatory insects. Experiments with hops, an important crop for the brewing industry, revealed that four times as many species of predatory insects were attracted when controlled release dispensers of methyl salicylate were placed in the field. This resulted in an equally dramatic drop in the number of spider mites, the primary arthropod predator of hops. [7] The predatory insects evidently developed methyl salicylate sensors as a means of locating an easy meal of mites. Everything is connected to everything else in ecology.

Oil of wintergreen is toxic and therefore potentially deadly at high dosage. One 5 milliliter teaspoon of oil contains 6 grams of methyl salicylate, comprised in part from salicylic acid. Aspirin, the first commercial analgesic,  owes its effects to the release of salicylic acid originally extracted from willow trees (genus Salix). One teaspoon of wintergreen oil is the equivalent of swallowing twenty aspirin pills (the normal dose is two tablets every 6 hours). Since ingested chemicals are spread throughout the body once absorbed through the walls of the small intestine, doses are normalized to body weight using the ratio of milligrams per kilogram, the equivalent of parts per million (ppm). A dose of 100 mg/kg can be fatal. As an example, only 3 grams or half a teaspoon of oil of wintergreen would be a potentially fatal dose for a child weighing 30 kilograms (about 65 pounds). [8]  A popular medicinal field guide includes the caveat that oil of wintergreen is “highly toxic;absorbed through skin, harms liver and kidneys(emphasis in the original). [9]

In spite of its toxicity, wintergreen is edible. The minute amount of methyl salicylate in the leaves and berries is well below the threshold for harmful effects in mammals and birds. It is the volatility of methyl salicylate that imparts the pleasant smell and taste of wintergreen that attracts them. The taste is perceived from the aroma since there are only five taste receptors: sweet, sour, salty, bitter, and savory; there is no wintergreen. When the leaves or berries are chewed, the released volatiles ascend through passages from the mouth to the olfactory epithelium in the nasal cavity that connects to the brain where scent information is processed. There are essentially an unlimited number of different aroma combinations and wintergreen is one of them. From the human perspective, wintergreen tea has been a North American staple ever since the colonists adopted the practice from Native Americans. Wintergreen berries consumed directly or made into pies and jellies have the same provenance. The wintergreen flavor, now mostly a food industry additive made from either laboratory produced methyl salicylate or black birch trees (which also contain methyl salicylate), is widely used in chewing gum and other consumer concoctions. Wintergreen is an important food source for birds, particularly ground dwelling species like the ruffed grouse, comprising over 2 percent of their food intake year-round. Among mammals, wintergreen browse is estimated to comprise about 5 percent of total food input for white-tailed deer, particularly further north. Wintergreen berries constitute up to 2 percent of the diet of black bears. [10,11]

Medicinal is the middle ground between toxic and edible. From the dose perspective, size matters. An amount of oil consumed and distributed in a large body can in its diluted state can prevent smaller animals like microbes from proliferating. Since methyl salicylate/oil of wintergreen probably arose as a deterrent to insects, that faculty persists. Most if not all antiseptic mouth washes contain methyl salicylate, listed on the label as anti-gingivitis and anti-plaque, killing the causative bacteria. Wintergreen leaves, while they may be eaten whole by deer, show no evidence of insect chewing. Apparently, the taste or smell suffices to deter them. Some of the “family friendly plant based” insect repellents that eschew DEET contain wintergreen oil, taking advantage of this effect. Based on personal experience, these natural chemical sprays work better than their industrial counterparts in deterring the confounding cloud of gnats that dive bomb into eyes and ears. This makes sense because plant chemical shielding is based on millennia of trial-and-error mutations and those chemicals that persist in living plants must have been effective.  Two comments about gnats ― a loose, descriptive term for small flying insects. First, there is a reason that they home in on eyes and ears. This must also be scent-based chemical attraction, in all likelihood an ingredient necessary for gnat sex according to their Kamikaze persistence. Second, gnats consist of multiple species all with their own evolutionary history and there is therefore no single chemical that will deter them en masse. This is why the so-called natural sprays, which can contain geranium oil, soybean oil, castor oil, cedarwood oil, citronella oil, peppermint oil, and lemongrass in addition to wintergreen oil, work better than chemical sprays, which mostly contain just DEET, most effective against ticks and mosquitoes.

Oil of wintergreen is an effective and potent pain medication. Methyl salicylate and its derivative salicylic acid are demonstrably one of the best treatments for everything from aching joints to migraines. Given the rudimentary understanding of the nervous system and pain propagation, the actual mechanism remains a mystery but surely it has something to do with neurotransmitters and receptors. Aspirin was the only commercial pain killer until the advent of ibuprofen (Advil), acetaminophen (Tylenol), and naproxen (Aleve) starting in the mid 1970’s. Native Americans used wintergreen broadly for a wide variety of ailments. Cherokees chewed the leaves for sore gums and to alleviate the symptoms of dysentery in addition to a substitute for chewing tobacco (which also contains methyl salicylate). The more northerly Iroquois Confederation tribes used wintergreen as a topical treatment for arthritis and rheumatism and internally as blood purifying tea.  In many cases, the specific treatment employed a concoction of several different herbs including wintergreen; its contribution to salubrity is moot.[12] There is some science here, however. A randomized double-blind trial with 182 participants with acute pain conducted using “topically applied rubefacients containing salicylates” to one group and a placebo to the other resulted in a 50 percent pain reduction. Similarly, a trial with 429 participants with chronic musculoskeletal and arthritic pain yielded a moderate but lower pain reduction. [13] One must conclude that oil of wintergreen is one of the few validated herbal remedies; it actually works.

References: 

1. Niering, W and Olmstead, N, National Audubon Society Field Guide to North American Wildflowers, Alfred A. Knopf, New York, 1998, pp 496-510.

2. Goff, S and Klee, H “Plant Volatile Compounds: Sensory Cues for Health and Nutritional Value?” Science Volume 311 Issue 5762, 10 February 2006, pp 815-819.

3. http://chemister.ru/Database/properties-en.php?dbid=1&id=2994

4. https://hort.purdue.edu/newcrop/med-aro/factsheets/WINTERGREEN.html     

5. Pichersky, E. “Plant Scents” American Scientist Volume 92 Number 6, November – December 2004, p 514.

6. Leslie, M. “At Long Last, Pathologists Hear Plants’ Cry For Help” Science, Volume 318 Issue 5847, 5 October 2007, pp 31-32.

7. James, D. and Price, T.  “Field-testing of methyl salicylate for recruitment and retention of beneficial insects in grapes and hops” Journal of Chemical Ecology 30 August 2004, Volume 30 Number 8 pp 1613–1628.

8. Tidy, C “Salicylate Poisoning” Patient Professional Articles 2014 at https://patient.info/doctor/salicylate-poisoning  

9. Foster, S. and Duke, J. Peterson Field Guide Medicinal Plants and Herbs, Houghton Mifflin Company, Boston, 2000, p 31.

10. https://wildadirondacks.org/adirondack-wildflowers-wintergreen-gaultheria-procumbens.html

11. Angier, B. Edible Wild Plants, Stackpole Books, Mechanicsburg, Pennsylvania, 2008, p 262.

12. The ethnobotany Native American database lists all documented uses of drugs by different tribes. http://naeb.brit.org/uses/search/?string=gaultheria+procumbenshe   

13. Mason, L.et al “Systematic review of efficacy of topical rubefacients containing salicylates for the treatment of acute and chronic pain” British Medical Journal 24 April 2004 Volume 328 Issue 7446 p 995.

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