Species native to North America - differs from Acorus calamus mainly in that it doesn't contain beta-asarone. In 1968 the FDA banned Acorus calamus from human food or food additives because of the presence of beta-asarone - several studies found it to be procarcinogenic in rats. Acorus calamus has a single prominent leaf vein running down the center of it's leaves; A. americanus has 2 or more less distinct veins running the length of it's leaves. See Acorus calamus for further discussion and uses.