Acorus calamus, commonly known as sweet flag is a tall perennial wetland monocot of the Acoraceae family, in the genus Acorus.
Sweet Flag is native to India, central Asia, southern Russia and Siberia, and perhaps Eastern Europe. It also grows in China and Japan. It was introduced into Western Europe and North America for medicinal purposes. Habitats include edges of small lakes, ponds and rivers, marshes, swamps, and wetlands.