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Sweet flag

Scientific name: Acorus americanus

Based on DNA sequence evidence, sweet flag (Acorus americanus) is of the oldest extant (living) lineage of Monocots (Duvall et al., 1993; Grayum, 1987). Monocots are distinguished as having a single embryonic leaf. Eudicots, the bulk of flowering plant species, have two leaves. The monocot group contains all orchids and grasses.

Acorus americanus grows in marshes and along the edges of ponds and lakes. Specimens of Acorus from central Siberia with similar leaf venation have been examined; this species may be holarctic (encircling arctic) in distribution (Motley, 1994; eflora 2005). It has large, flat, grass-like leaves, which are distinctly aromatic when crushed. Its flowers are brownish-green and arranged on cylindrical spikes (See photo to right). Flowers are bisexual (containing both male and female reproductive organs) with 6 stamens (male organ) and 1 ovary (female organ). Sweet flag is considered to have tepals (6 in total), rather than distinct petals or sepals. The fruit is a reddish brown berry with few seeds. Acorus americanus rarely blossoms and instead propagates vegetatively from creeping branched rhizomes (swollen underground stems (Rook, 2004; Siegel-Maier, 2005; MicropsyU, 2005)

Acorus species have been important throughout human civilization. In the Far East and Egypt, its was consdered a powerful aphrodisiac. Turk's historically carried it to thwart infectious disease. The Dutch ground the rhizome for medicinals, tea, chewing gum, candy, and dry shampoo. In Europe it was used to flavor alcohols, toothpaste, and to powder wigs. In North America, Native Americans used it ritually and to treat respiratory disorders. Shakers added it to medicinals for coughs, bronchial congestion and toothaches. Today, sweet flag is used by Chinese herbalist to lower blood pressure and treat epilepsy. In India, it is used to check asthma (Siegel-Maier, 2005; MicropsyU, 2005).

In the field of botany, there is constant revision in plant systematics (the classification of plants according to evolutionary relationships). Today, plant systematists recognize many more species of Acorus, where previously no distinctions were recognized (Vandaveer, 2005). Although scientific names were adjusted to reflect this knowledge, many species continue to share the same common names. Additionally, species are notoriously hard to tell apart. In North America an introduced species from Eurasia (Acorus calamus) is often confused with Acorus americanus. Rats fed varied levels of this sweet flag developed heart and liver abnomalities within a few months and later intestinal tumors. For this reason “sweet flag’ is banned from all products intended for human consumption in the United States. (Siegel-Maier, 2005).

Author: Heather Fara, University of Florida. Send comments or corrections


Native to New Caledonia

Map: The red area indicates reported occurrence of Acorus americanus. Siberia is only tentatively included, as taxonomic work is still needed to confirm that species designations are equivalent. Map created by Heather Fara, University of Florida.

flowerstem tissue

Photos: (a) Flower, property of the Floral Genome Project, fgp.bio.psu.edu/fgp. (b) Stem tissue under confocal microscope, Nathan Claxton et al., the National High Magnetic Field Laboratory, Florida State University.


Duvall et al. (1993) Phylogenetic Hypotheses for the Monocotyledons Constructed from rbcL Sequence Data. Annals of the Missouri Botanical Garden 80(3):607-619.

eFlora (2005) Acoraceae, Acorus americanus FNA Vol. 22 Version: 17 Nov 2005. www.efloras.org

Grayum (1987) A summary of evidence and arguments supporting the removal of Acorus from the Araceae. Taxon 36:723--729.

Thompson, S. A. 1995. Systematics and Biology of the Araceae and Acoraceae of Temperate North America. Ph.D. dissertation. University of Illinois - Urbana-Champaign.

Motley (1994) The ethnobotany of sweet flag, Acorus calamus (Araceae). Econ. Bot. 48: 397--412. Packer, J. G. and G. S. Ringius. 1984. The distribution and status of Acorus (Araceae) in Canada. Canad. J. Bot. 62: 2248--2252.

MicropsyU (2005) Phase Contrast and DIC Comparison Image. Small World Gallery. www.microscopyu.com/galleries/dicphasecontrast

Rook (2004) Acorus americanus. The Boundary Waters Compendium. Version: 14 Nov 2005. www.rook.org/earl/bwca/nature/aquatics/acorus.html

Siegel-Maier (2005) Sweet Flag. Suit101.com Version: 10 Jan 2006

Vandaveer (2005) How the plant got here? www.killerplants.com/weird-plants/20020516.asp

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