AC'ORUS (Gk. ἄκορος, akoros, sweet-flag). A genus of plants of the natural order Araceæ. (See Arum.) The plants of this genus have a leaf-like scape, which bears upon its side a dense, cylindrical, greenish spike of flowers. Here belongs the Sweet-flag (Acorus calamus), which was brought to Europe from Asia in the fifteenth century, but has become naturalized in England, Germany, etc., growing in marshes and ditches. In North America it is found from Nova Scotia to Florida, and west through Minnesota and Iowa. Its root (rhizome) is perennial, divided into long joints about the thickness of the thumb, has a bitterish, acrid taste, and is very aromatic. It is a powerful medicine of transient tonic effect, occasionally used, especially in cases of weak digestion. In many places on the Continent of Europe it is found in confectionery shops sliced and prepared with sugar. It is also used to correct the empyreumatic odor of spirits and to give them a peculiar flavor. It is called Calamus root. In Great Britain it is chiefly employed by perfumers in the manufacture of hair powder. The other species of Acorus are likewise aromatic, and are applied to the same uses. Acorus gramineus is cultivated in China. Some fossil species of Acorus have been found in rocks of the Tertiary Age in North America and on the island of Spitzbergen, and in later formations in other parts of the world.