Sweet flag or Acorus calamus is a shrub commonly found in India, but it is also found in many parts and climates of the world. It is found in Europe, in southern Russia, northern Asia Minor, southern Siberia, China, Japan, Burma, Sri Lanka, and northern USA.

This tree is a member of Acoraceae plant family.

This is a small acquatic or marsh herb wwith flashy tuberous, creeping, aromatic root stocks. The leaves are distichous, narrow grass like or sword shaped, long and slender without distinction of petiole and parallel veins. The spadix are sessile, spathe are as long as leaves. The flowers are bisexual with perianth of concave hooded segments, stems are 6 anthers flattered. The ovary is 2-3 celled with 2 ovules in each cell. The stigma is sessile.