Acorus americanus (Raf.) Raf - American Sweetflag


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Acorus americanus - (image 1 of 5)



Family: Acoraceae


Shallow waters of stable marshes, swamps, river and streams. Populations tend to be more localized than those of A. calamus.




Newfoundland south to VA, west from AK to WA.


Leaves all basal, crowded at the base, glossy yellow-green, reddish at the base, with a wide central raised area running most of the length of the leaf, the midvein not much raised relative to the adjacent veins. Flowers tiny, yellow-brown, in a greenish spadix borne on a leaf-like scape.


Flowers mid May to July

Wetland Indicator: Obligate

The rhizomes of this pleasantly aromatic plant can reportedly be made into candy (Peterson, 1997). The roots are peeled, cut into short lengths, and boiled in several changes of water for about an hour or until tender, then simmered in a rich sugar syrup for 20 minutes and set aside to dry.

Historically this species was often regarded as synonymous with A. calamus (sometimes also as the variety americanus). Because of this the distribution of this species may not be fully understood. Triploid and tetraploid cytotypes of A. calamus produce the carcinogen β-asarone and other toxic phenylpropane derivatives; diploid cytotypes of A. calamus and A. americanus lack these compounds (Motley, 1994).

The triploid form of Acorus calamus L. has become naturalized in Eastern North America, presumably from Europe. It is typically larger in size, with leaves that tend to be broader and flatter, with a single prominent midvein slightly offset from the center of the leaf; the margin on one side of the larger leaves is also often wrinkled. It can form extensive colonies in fens and other moist open sites. Although it does not produce viable seed, it has managed to become established over a rather wide range in the east; it is possible that it disperses vegetatively via fragmented rhizomes. Diploid forms of A. calamus are found in Eastern Asia, while the tetraploid is found in India, Siberia and Japan (Flora of China, 2014).

Acorus calamus



Flora of China, Vol. 23. Acorus calamus. Accessed 2, Aug, 2014.


Motley, T. J. 1994. The ethnobotany of sweet flag, Acorus calamus (Araceae). Economic Botany 48(4): 397-412.


Peterson, L. A. 1977. A Field Guide to Edible Wild Plants: Eastern and central North America.

Houghton Mifflin Company. New York, NY


USDA, NRCS. 2002. The PLANTS Database, Version 3.5 (
National Plant Data Center, Baton Rouge, LA 70874-4490 USA




Michael Hough 2014