American Sweet Flag Acorus americanus

American Sweet Flag is an evergreen, herbaceous perennial, aquatic rush or sedge, native to Siberia and the cold regions of northern North America and often found in wet open areas, such as marshes, or along the edges of quiet water. It is a member of the sweetflag family (Acoraceae) and, at maturity, can reach a height of 3 to 4 feet. The leaves have a citrus-like aroma, are white at the base, and usually green above, although there is sometimes a reddish or pink tinge at the base. Yellow inconspicuous flowers, 1 to 3 inches, bloom in spring and early summer.

The genus name comes from the Greek for pupil, because the plant was used to treat inflammation of the eye. The species name indicates that this is an American species of the genus. In particular, it differentiates it from the similar, European species, A. calamus. The plants are so similar that A. americanus is sometimes considered a variety of A. calamus. 

American Sweet Flag is a freshwater aquatic plant that grows best in wet sites with full sun and does not tolerate shade. It does well in boggy conditions (shallow standing water up to 9 inches deep) and consistently moist garden soils. It will spread, at a moderate rate, by means of rhizomes. Kew Garden, which tracks the worldwide distribution of plants, notes that the plant has gone extinct in the southern part of its range (Virginia and states further south) and it is listed as a protected plant in Pennsylvania.

To grow in a water garden, plant the rhizomes in moist soils at the water’s edge or in containers set in shallow water. Rhizomes or existing clumps can also be planted in containers sunk into wet boggy areas.  

Sweet Flag rhizomes and plants were valued by early Native American groups and were objects of trade and this probably led to the wide distribution of the plant across Canada and the United States. Plant populations often occur near old Native American village sites or camping areas.

Diseases, Insect Pests, and Other Plant Problems:

Susceptible to infection by Uromyces sparganii fungus.

More information on Acorus calamus.