Calamus

Acorus calamus, commonly known as sweet flag, is a perennial and semiaquatic plant with creeping rhizomes. Sweet flag consists of tufts of basal leaves that rise from a spreading rhizome. It can be distinguished from iris and other similar plants by the crimped edges of the leaves, the fragrant odor it emits when crushed, and the presence of a spadix. It grows wild along swampy and marshy areas in the northern temperate and subtropical regions of Asia, North America and Europe. Calamus leaves and rhizomes contain a volatile oil that gives a characteristic odor and flavor.

Three cytotypic forms are distinguished by chromosome number: a diploid form (2n=24), an infertile triploid form (2n=36), and a tetraploid form. Plants in North America are generally diploid, those in Europe and temperate Asia are primarily triploid, and those in eastern and tropical Asia are tetraploid. The taxonomic position of the different forms is contested. One analysis considers all three forms to be distinct varieties of a single species, and another considers the diploid form to be a distinct species.

The proportion of each chemical component in the oil varies among the varieties, depending on the degree of polyploidy. Beta-asarone may form up to 96% of the essential oil in tetraploid Asiatic plants and up to 5% of the oil in triploid European plants. It is absent or undetectable in diploid North American plants. The oil is a source of oxygenated sesquiterpenes of great structural variety. The major constituents of the oil include beta-asarone, methyleugenol, cis-methylisoeugenol, geranylacetate, beta-farnesene, shyobunone, epishyobunone, isoshyobunone, calamusenone and acorenone.

In oil from rhizomes grown in Estonia, beta-asarone (85.3%) was the major constituent in one sample, a characteristic of tetraploid plants. Two other samples, probably triploid, had lower beta-asarone but more acorenone (22.4-27.5%), shyobunone (8.2-13.7%) and preisocalamendiol (8.1%). Oil of rhizomes obtained from China had alpha-asarone (50.09%), (E)-methylisoeugenol (14.01%), methyleugenol (8.59%) and beta-asarone (3.51%) among its main components. Oil of rhizomes collected from Italy contained acorenone (21.6%), shyobunone (7.0%) and alpha-asarone (5.1%) among others. Oil of the plant collected in Quebec, Canada contained preisocalamenediol (18.0%), acorenone (14.2%), shyobunone (13.3%) and cryptoacorone (7.5%). Across 27 genotypes from India, the beta-asarone content of the oil ranged from 65.96% to 92.12%.

A 2001 ruling by the European Commission recommended limits on consumption in food or alcoholic beverages of 115 micrograms per day, but the degree of safe exposure remained undefined. In Ayurveda, the rhizome is used only after a purification step (shodhana), in which it is boiled in media such as cow's milk. The roots can be washed, peeled, cut into small pieces, boiled, and simmered in syrup to make candy. The rhizome has shown insecticidal activity against a wide range of insect species. The plant is sometimes used as a pond plant in horticulture.

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