Acorus americanus (Sweet-flag)
|Also known as:
|sun; silty soil in quiet water to 20 inches deep; ponds, lakes, marshes
|June - July
|2 to 6 feet
|Wetland Indicator Status:
|GP: OBL MW: OBL NCNE: OBL
|MN county distribution (click map to enlarge):
|National distribution (click map to enlarge):
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Leaves and stems:
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.
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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Photos by K. Chayka and Peter M. Dziuk taken at Sucker Lake, Ramsey County.
Have you seen this plant in Minnesota, or have any other comments about it?