Acorus americanus (Sweet-flag)

Plant Info
Also known as:
Genus:Acorus
Family:Acoraceae (Sweet-flag)
Life cycle:perennial
Origin:native
Habitat:sun; silty soil in quiet water to 20 inches deep; ponds, lakes, marshes
Bloom season:June - July
Plant height:2 to 6 feet
Wetland Indicator Status:GP: OBL MW: OBL NCNE: OBL
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

Pick an image for a larger view. See the glossary for icon descriptions.

Detailed Information

Flower: Flower shape: indistinct Cluster type: spike

[photo of flower heads] Tiny yellowish to brownish flowers cover a cylindrical, finger-like head 1½ to 4 inches long that protrudes from the middle of a stiff, erect, green leaf-like spathe.

Leaves and stems: Leaf attachment: basal Leaf type: simple

[photo of leaves] Leaves are basal, sword-like, 2 to 6 feet long and about ½ inch wide, bright green, with an off-center midvein that is slightly swollen in cross-section. The base of leaves are typically white or tinged red. Leaves are sweetly fragrant when broken.

[lateral leaf veins] 2 to 6 additional veins run parallel to the midvein, which are typically described as “raised”. While they may not be felt, they are visible when held up to the light and are raised on dried leaves.

Fruit: Fruit type: capsule/pod

[photo of fruit] Fruit is a tiny capsule, an inverted pyramid in shape, containing 2 or 3 seeds. Fruits dry to brown.

Notes:

A colony of Sweet-flag may resemble a stand of cat-tails or blue-flag iris but upon closer inspection the finger-like flower heads buried in the leaves make it easy to identify. There are 2 species of Acorus in North America: A. calamus, introduced from Europe and Asia, and A. americanus, the native Sweet-flag. In Minnesota, a good number of the herbarium records were labeled A. calamus, but it is suspected they are all really A. americanus and the DNR no longer recognizes A. calamus as being present in the state. A point of confusion, which I experienced myself, is the number of “raised veins” on the leaves, A. calamus having just one and A. americanus having multiples. On fresh leaves these veins are not so apparent. I mistook the midvein as the single vein, and assumed the population at Sucker Lake, where these images were taken, was A. calamus. Once a leaf specimen dried, however, the extra veins were obvious and I discovered that holding it up to the light showed them clearly even though they could not be felt.

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More photos

Photos by K. Chayka and Peter M. Dziuk taken at Sucker Lake, Ramsey County.

Comments

Have you seen this plant in Minnesota, or have any other comments about it?

Posted by: Steve - Northern Minnesota - probably somewhere on Rainy Lake
on: 2015-02-17 10:25:24

In the 70s, I was a fan of Euell Gibbons' books, and always had my eye out to discover in nature one of the plants I had only read about. Pushing off the lake shore in a small boat, I was delighted to see the lush green leaves with that distinctive yellowish spadix jutting from the surface toward the top of the plant. I will never forget the wonderful spicy, lime-like fragrance that the leaves emitted when crushed, just as Gibbons had predicted. We took a few leaves back to our tent, enjoying their scent every time we stepped on them. I have been looking for them ever since then, without success.

Posted by: Andrea - Brookston
on: 2016-07-27 16:15:48

In a swampy bog.

Posted by: Brian - Ottawa WMA, Le Sueur County
on: 2018-02-02 13:08:11

There's a nice colony of sweet flag growing at the northern edge of the south pond at Ottawa WMA just east of the Minnesota River in Le Sueur County. Irises grow along with it.

Posted by: Susan Foss
on: 2020-12-28 11:39:07

Daniel Moerman says in "Geraniums for the Iroquois" page 189 that Sweet Flag was introduced early into North America. He is a PHD in ethnobotany at the U of Michigan. Comment?

Posted by: K. Chayka
on: 2020-12-28 13:25:02

Susan, there are two species commonly called sweet flag, one of which, Acorus calamus, was indeed introduced to North America. Latin names are always helpful in cases like this.

Posted by: Gilbert White - Hovland
on: 2021-06-10 17:12:19

The best description of the smell of the leaves, for good reason, is Dr Pepper. I am growing 15 gallon tubs full, started from seed. Supposedly A. calamus does not produce viable seed.

Posted by: Gilbert White - Hovland
on: 2022-07-16 11:14:38

Aka rat root to many Native Americans. Possibly introduced from Asia millenia ago. Apparently the A Americanus species exists in Buryats region near Baikal. The flavor of the leaves is Dr. Pepper. Brer Rabbit said disingenuously to Brer Fox, I don't eat no chicken less it's cooked with calamus root.

Posted by: Davis Harder - Jackson County
on: 2023-01-05 12:30:37

Found two populations in Jackson County in 2022.

Posted by: Doug McEvers - 3 miles NE of Barnesville, Clay County
on: 2023-03-20 14:50:18

While looking over one of our prairie remnants last summer, my prairie expert friend, Wendell Olson, found Sweet flag. It was growing in what I will call a small prairie pothole that has seasonal water in it. Also found were some interesting sedges and mints. I collected a few seed pods last fall and use in an upcoming prairie planting.

Posted by: Laura Segala - Fazendin Native Plant Pollinator Garden - Plymouth
on: 2023-08-09 16:28:42

Planted at the Fazendin Native Plant Pollinator Garden in Plymouth last year. There is a lower elevation portion in the middle of the garden that is pretty swampy in the spring and this is the spot where the Sweet-flag seems to be thriving.

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