by Erin Holden

While doing research for a presentation on herbal uses of native plants, I decided to look more into a plant I’d learned about in herb school, sweet flag (Acorus calamus). This strongly aromatic aquatic plant has long been my favorite warming digestive bitter for those times when I overindulge in a huge meal (I’m looking at you, Thanksgiving). The flavor is warm, pungent, bitter, and spicy in a black-peppery way – the flavor sort of fills up your mouth and is warm all the way down to your stomach. But as I dug deeper into the research, I discovered I’d been wrong all this time about the origin of the Acorus species I’d been using. It turns out that A. calamus is native to Europe, temperate India, and the Himalayan region, while the native species is A. americanus (also called sweet flag), although the two species look so similar that even some scientists are unsure of which species they’ve studied and reported on. There still isn’t much consensus among taxonomists as to what differentiates these two – some even classify them as the same species (Boufford,1993; eFloras, 2008). Let’s take a deeper look at the similarities and differences between these two plants. 

There are many common names for sweet flag from all over the world (Daglan, 2014), many of which describe either the flavor of the root (like bitter, sweet, pepper) or its watery habitat:

Abenaki: mokwaswaskw (muskrat plant)

Ayurvedic Tradition: vacha 

Cheyenne: wi’ukh is e’evo (bitter medicine) 

Chinese Medicine: shui chang pú (watery flourishing weed)

English: sweet flag, calamus 

Hudson Bay Cree: pow-e-men-arctic (fire or bitter pepper root) 

Penobscot and Nanticoke: muskrat root

Micmac: ig gig’wesukwul (muskrat root)  

Pawnee: kahtsha itu (medicine lying in water) 

Many Native American names connect Acorus with muskrats. According to Sue Thompson’s dissertation on Acorus (as reported by Daglin, 2014): 

There seems to be “a closely linked ecological relationship between Native Americans trapping muskrats and using Acorus, muskrats eating Acorus, and Acorus. Muskrat feeding habits may in part be responsible for the dispersal of Acorus, and Native Americans may have intentionally planted Acorus both for their own medicinal use and to ensure food for the muskrat, which was economically valuable to them (Morgan 1980). Thus, the many Native American names for Acorus, which involve muskrat as a root word, may reflect an important economic and ecological relationship among man, plants, and other wildlife.”

Both species are perennial, grow in zones 4 to 10, have 1’–3’ tall iris-like leaves, and can spread 1’–2’. They bloom April through June, and like full sun to part shade. The inflorescence is a green spadix with no spathe (a spathe is a hood-like structure, like the white part of a peace lily). Both A. americanus and A. calamus are freshwater aquatic plants that grow in medium to wet soil and can grow in up to nine inches of water. They’re both easily propagated by root/rhizome divisions in the spring. Since they are aquatic plants, they can be used in water gardens, ponds, or rain gardens. They can also grow in regular garden beds as long as they get adequate water, so they’re very versatile if you’re looking for tall, straight leaves (Missouri Botanical Garden, 2022).

Although the two species look very much alike, there are some subtle differences you can use to tell them apart. A. calamus has leaves with one prominent vein and undulate (wavy) margins, does not produce fruit, and will “appear to have a shriveled ovary” in late summer, whereas A. americanus has leaves with two to six veins and smooth margins, produces small green berries, and has swelling ovaries in late summer (Dalgin, 2014).

The two prominent veins and smooth margins of A. americanus

The prominent midvein and undulate margins of A. calamus

There are also some unseen differences between the two. It turns out that A. americanus is a fertile diploid species and contains almost no phenylpropanoids, a chemical family whose members play a role in the flavors and aromas of cinnamon, cloves, nutmeg, and sassafras. A. calamus is a (mostly) sterile triploid (there are some populations of a fertile diploid phenotype in Asia that are morphologically distinct from the North American A. americanus). In addition, 13% of its volatile oil fraction is made up of those phenylpropanoids, one of which is β-asarone.

This chemical distinction is important, because β-asarone has demonstrated procarcinogenic tendencies (meaning it could metabolize into a cancer causing compound), and the FDA has banned the use of “calamus, calamus oil, or extract of oil in food,” although these studies used high levels of isolated β-asarone and not “suggested doses of the whole plant in terms of mg/kg of body weight” that an herbalist would recommend. However, since A. americanus has little to no β-asarone, it’s been suggested that this species is safe to consume (Dalgin, 2014).

Sweet flag is an important plant for many native peoples. One writer said it is “considered so sacred [to the Cheyenne] that only qualified Sundance priests [can] collect it,” and it “may be the most important herb in Penobscot pharmacology” (Dalgin, 2014). 

Historically, the Dakota used a paste on their faces to “instill fearlessness and provide stamina” in battle and chewed the rhizomes to enhance endurance “during the wars of the 20th century” (Dalgin, 2014). 

Other uses for the plant include: colds, flu, and sore throat; as a tonic; for intestinal pain and as a carminative (dispels gas); as a stimulant when tired; toothache; an analgesic for muscle cramps/spasm; and in ceremonial/religious rituals.

Colonists also used Acorus, and Eclectic physicians (doctors in the 1800s) incorporated it into their materia medica (list of medicinal substances). Eventually, it made its way into the first edition of the  Dispensatory of the United States in 1833 (Osol et al, 1833), which cataloged drugs used by U.S. pharmacists at the time. These groups used it pretty much the same way that Native Americans use it: as a carminative, for weak digestion and flatulent colic, as a sialagogue (stimulates saliva production) and as “breath perfume,” a warming aromatic bitter, and externally for ulcers that wouldn’t heal (Dalgin, 2014). 

Some modern herbalists who use both species say that, because of its higher volatile oil content, A. calamus targets the gastrointestinal system more specifically, while A. americanus has a “more balanced” action on the whole body—working equally on the gastrointestinal and nervous system, as an expectorant (which helps clear gunk from the lungs), spasmolytic (calms spasms), and antitussive (Daglin, 2014).

Now that I know about A. americanus and its different effects on the body, I’m interested in experimenting with the two species. I’ve also planted it out in the Native American bed in the National Herb Garden. I wonder if we should also invest in a muskrat.

Photo Credits: 1) Acorus calamus inflorescence (E. Holden); 2) Muskrat (Linda Tanner, via Wikimedia ); 3) Acorus sp. used as a mass border planting (KENPEI, via Wikimedia  ); 4) Two prominent veins and smooth leaf margins of A. americanus (E. Holden); 5) The prominent midvein and undulate leaf margins of A. calamus (E. Holden); 6) Botanical illustration of A. calamus (Creative Commons, Rawpixal LTD); 7) Acorus americanus growing along a stream bank (Ryan Hodnett, via Wikimedia)

Medicinal Disclaimer: It is the policy of The Herb Society of America, Inc. not to advise or recommend herbs for medicinal or health use. This information is intended for educational purposes only and should not be considered as a recommendation or an endorsement of any particular medical or health treatment. Please consult a health care provider before pursuing any herbal treatments. 

References 

Boufford, D. E. 1993+. Acorus. In: Flora of North America Editorial Committee, eds. Flora of North America North of Mexico [Online]. 22+ vols. New York and Oxford. Vol. 3. Accessed 10/5/22. Available from http://beta.floranorthamerica.org/Acorus

Dalgin, R. 2014. Acorus calamus and Acorus americanus. Integrative Herbalism: Journal of the Vermont Center for Integrative Herbalism. Summer, 30-78.

eFloras. (Internet). 2008. Acorus calamus. Missouri Botanical Garden, St. Louis, MO & Harvard University Herbaria, Cambridge, MA. Accessed 10/5/2022. Available from http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=200027130

Lady Bird Johnson Wildflower Center. (Internet). 2015. Acorus americanus (Raf.) Raf. Accessed 1/7/2022. Available from https://www.wildflower.org/plants/result.php?id_plant=ACAM

Missouri Botanical Garden. 2022. Acorus calamus. Accessed 1/7/2022. Available from https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=276172

Orsol, A., C. H. LaWall, F. Bache, G. B. Wood, G. E. Farrar, H. C. Wood Jr., and J. P. Remington. The dispensatory of the United States of America. Grigg & Elliot: Wisconsin. Available from https://www.google.com/books/edition/The_Dispensatory_of_the_United_States_of/xikzAQAAMAAJ?hl=en&gbpv=1

Erin is the gardener for the National Herb Garden at the U.S. National Arboretum in Washington, D.C. She is a member of the American Herbalists Guild, United Plant Savers, and a member-at-large of the Herb Society of America.