sweet flag

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A perennial herb (Acorus calamus) native to Eurasia and naturalized in North America, growing in marshy places and having grasslike leaves, minute greenish flowers borne on a thick spadix, and aromatic rhizomes used in medicine and perfumery.
• noun A similar plant (Acorus americanus) native to North America.

from The Century Dictionary.

• noun An araceous plant, Acorus Calamus, with sword-shaped leaves and two-edged leaf-like scapes, from one edge of which emerges a cylindrical spadix.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun a perennial wetland plant, Acorus calamus, with an aromatic medicinal root, formerly used to strew floors, also known as calamus

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun perennial marsh plant having swordlike leaves and aromatic roots