Narrow-leaf mountain mint (Pycnanthemum tenuifolium) is a lesser-known member of the mint family (Lamiaceae) because unlike thyme, oregano, basil, rosemary, mint, sage or marjoram, it is not a widely cultivated and used culinary herb. Some mountain mints may not even be safe to consume. Narrow-leaf mountain mint demonstrates that despite mint family members having already proven their value for food, cosmetics, flavoring, fragrance, pesticide, and pharmaceutical applications, this astonishing plant family is still likely underutilized.
Mountain mints in general are becoming more accepted as garden plants, increasingly recognized as non-aggressive members of the mint family with visually interesting foliage and plentiful flowers attractive to a wide array of insects.
Rubbing mountain mint on skin has been reported to be a natural mosquito repellent. Because the plant’s repellant properties are likely related to essential oil chemistry and because the essential oil content of Pycnanthemum varies by species and range (Betz et al., 2016), the degree to mountain mint effectively repels mosquitos likely also varies by Pycnanthemum species and range.
“Butterflies, bees, moths, beetles … everyone comes for a visit, especially insects you’ve never seen before. I suggest grabbing your kids and cataloging the unique insect species that drop by — the range is unlike any other native perennial’s.”
-Benjamin Vogt, 2013
Mountain mint’s genus, Pycnanthemum, includes only species native to the Americas. Narrow-leaf mountain mint can be distinguished from other mountain mints by its linear leaves with distinct midribs that are less than 1/4-inch wide and often much narrower. Pairs of leaves grow opposite from each other along the stems.
Small white or light pink flowers are tightly clustered on the ends of stems and are structured in a way that wasps and other short-tongued insects can easily feed on them. The bloom time of the flowers is staggered which leads to a months-long blooming period.
Stuff Almost Nobody Knows:
(for the perpetually curious)
Some plants are better for pollinators than others but understanding exactly which plants are best for pollinators and under what conditions is far less clear. Studying this question requires detailed, repetitive work. Studies like the pollinator trials conducted by the Penn State Master Gardeners between 2011 and 2015 yield insight even if the degree to which results can be extrapolated isn’t fully agreed. During this study, 4500 plant plugs representing 86 species and cultivars of native plants were planted, grown out and then, over subsequent years, monitored for insect visitation, vigor and blooming on a weekly basis (Penn Sate Dept. of Entomology, 2016). A wide range in pollinator visits per plant and diversity of pollinators per plant was observed. The most frequently visited species received an order of magnitude more pollinator visits than many less frequently visited species (Figure 1). The species which attracted the greatest diversity of insects attracted twice as many types as the species which attracted the least (Figure 2). While narrow-leaf mountain mint was not included in the study, clustered mountain mint (Pyncanthemum muticum) dominated the rankings in terms of both frequency of pollinator visits and diversity.
Clustered mountain mint dominating the rankings is particularly noteworthy because this study wasn’t designed to discover what kinds of plants attract pollinators. All the plants included this study were already known to attract pollinators. This study was designed to find “the best of the best”. Based on these study results combined with an abundance of anecdotal observations from individual long-time gardeners who note that they have observed insects they have never seen before on their mountain mints, it is reasonable to conclude that mountain mints are capable of attracting both an unusually large number of insects and an unusually broad diversity of insects.
While it is clear how an abundance of pollinators would help plants successfully cross-pollinate, it is less clear how attracting a diversity of pollinators helps. Many plants have adopted the opposite strategy and evolved to be highly attractive to just one type of pollinator or just a few types of pollinators compared to attracting as many as possible. Ecological specialization of flowers is often referred to as ‘specialized pollination’. The idea behind specialized pollination is that the more exclusive the relationship is between plant and pollinator, the greater the likelihood of efficient pollen transfer due to the increased probability that the pollinator will sequentially visit flowers of the same type. Mountain mints pay a price for their lack of flower specialization. This price manifests as the energy requirement associated with supporting a long flowering period, copious flower production and, presumably, a disproportionately high rate of nectar production.
Perhaps the only reward mountain mints receive for providing support to a large and diverse group of insects is a reduction in the risk of a preferred pollinator not showing up. Perhaps the story is more complicated. A plant which attracts an abundance of insects and a disproportionately wide range of insects also attracts a disproportionately wide range of predatory or parasitoid insects. In healthy ecosystems, natural enemies keep pests and potential pests under control. The relationship between plants and insects isn’t as simple and pleasant as a mutually beneficial exchange of nectar for pollination service. Some insects eat plant leaves, some bore into plant roots, some eat pollen, some suck out plant juices and some transmit plant diseases or infections. Perhaps the diversity of insects supported by mountain mints provides a type of local pest control service which benefits both the mountain mints and the local ecosystem in general.
Whether an insect is a pest or a beneficial ecosystem contributor depends on local conditions and local conditions may change. The risk that an insect could act as a pest is not new. However, with the onset of global trade and in particular the global horticultural trade, this risk may be at an all-time high because not only do ecosytems need to continue to control potential native pests, worrisome non-native insects show up regularly. Fifty to seventy percent of invasive and naturalized species arrived in their new lands via the horticulture trade (Marinelli, 2020). In fiscal year 2020 alone, U.S. Customs and Border Protection reported 31,785 incidents of detecting some pest (Milius, 2021). If 31,785 pests were detected, certainly many slipped through the net.
Predatory and parasitoid insects have probably been providing a defense against both native and non-native insect pest incursions for as long as the threat has existed. If the threat level has increased, it makes sense increase the level of defense against the threat. A plant that provides local pest control likely disproportionately contributes to overall ecosystem resilience and the value of resilience increases during times of instability. We are living in ecologically unstable times. If mountain mint has the capability to strengthen ecosystem resilience, the time to recruit the mountain mints into a position of greater service is right now.
Black Squirrel Farms strives for accuracy but everyone makes mistakes sometimes. We’re happy to update our information if needed. Please contact us if you spot an error or have a suggested edit, update or information inclusion. Help is welcome.
Betz, Susan and Knapke, Debra and Schlosser, Kathy and Stravinsky, David and Wells, Linda, 2016. “The Herb Society of America’s Notable Native 2016 – Mountain Mints”, http://www.ncherbsociety.org/uploads/8/4/4/3/84437124/pycnanthemum_nn_2016.pdf
Marinelli, Janet, 2020. “Non-native plants are hurting the birds and bees”. GreenBiz, https://greenbiz.com/article/non-native-plants-are-hurting-birds-and-bees, Dec 29, 2020.
Milius, Susan, 2021. “Focusing on Asian giant hornets distorts the view of invasive species”. Science News, https://www.sciencenews.org/article/asian-giant-murder-hornet-invasive-species-ecology, July 1, 2021.
North Carolina Botanical Garden, 2019. “2019 Wildflower of the Year, Narrow-leaf mountain-mint, Pycnanthemum tenuifolium“, https://ncbg.unc.edu/2019/05/30/2019-wildflower-of-the-year-narrow-leaf-mountain-mint/
Penn State Department of Entomology, 2016. “Bees, Bugs & Blooms – A pollinator trial”. https://ento.psu.edu/news/bees-bugs-blooms-2013-a-pollinator-trial
Vogt, Benjamin, 2013. “Great Design Plant: Virginia Mountain Mint”, houzz.com magazine, https://houzz.com/magazine/great-design-plant-virginia-mountain-mint-stsetivw-vs~5967773.