Acorus americanus

Sweet Flag

Sweet Flag, Photo © by Earl J.S. Rook
Sweet Flag
Photo © by Earl J.S. Rook

Flora, fauna, earth, and sky...
The natural history of the northwoods


  • Acorus, the Latin form of the Greek 'akoron (akoron), presumably an ancient plant name for the Sweet Flag or the Yellow Flag Iris (Iris pseudacorus)
  • americanus, from the Latin, "of America", to distinguish the native species from the virtually identical Eurasion Acorus calamus (calamus, from the Greek, kalamos (kalamos), "reed")
  • Sweet Flag, from the sweet fragrance of the bruised leaves, and their similarity to the leaves of iris, also known as flag (eg, Blue Flag, Iris versicolor).
  • Other common names include: Calamus, Flagroot, Myrtle Flag, Sweet Sedge, belle-angelique (Qué), shih-ch'ang pu (Chi), Kalmus (Dan, Ger, Swe), Groene Kalmoes (NL), Kalmojuuri (Fin), Bachh (Hindi), Calamo Aromatico (It), Kalmusrot (Nor), Racha (Vedic)


  • Kingdom Plantae, the Plants
    • Division Magnoliophyta, the Angiosperms (flowering plants)
      • Class Liliopsida, the Monocotyledons
      • Subclass Arecidae
        • Order Arales
          • Family Acoraceae, the Sweet Flags (sometimes with Araceae)
            • Genus Acorus, the Sweet Flags
  • Taxonomic Serial Number: 42523
  • Also known as Acorus aromaticus, Acorus calamus, Acorus calamus var. americanus
  • Some measure of confusion exists over the taxonomic the status of Acorus in North America. Whether native or introduced, whether one or more species, have been among the questions. Recent studies of morphology, essential oil chemistry, cytology, isozymes, and ethnobotany suggest the existence of two species in North America -- Acorus calamus, an introduced Eurasian species and Acorus americanus, the native Sweet Flag. The Integrated Taxonomic Information System (ITIS) lists the accepted name of North American Sweet Flag as Acorus americanus (TSN182561). Because all Sweet Flag in North American has long been lumped together as Acorus calamus, especially in the popular, non-professional realm, expect the confusion to continue.
  • Although historically considered an aberrant genus within the family Araceae, recent evidence based on DNA sequences fails to show any close relationships between Acorus and other genera, and instead supports Acorus as the oldest surviving line of monocots. So despite its sparse fossil record, the group has great importance for paleontologists, providing one picture of what early monocots may have looked like.


  • A hardy perennial swamp or bog plant with sweet, spicy-scented leaves.
  • Leaves sword-shaped, erect in clumps, usually about 2' tall but twice that in rich soil. Bright yellow-green for most of their length; white with pink or red at the base. Leaf shows 2-6 major veins, more-or-less equally raised above the leaf surface. Leaf cross-section thickened in center, tapering to sometimes crinkled edges. Crushed leaves exude distinct tangerine odor.
  • Rootstalk creeping, with brownish-red bark and a white, fleshy interior. Usually 1"-2" thick, it can spread several feet in mature plant.
  • Flower a cylindrical spike (spadix), 2"-4" long and studded with tiny greenish-yellow blossoms; angles out near the base of the leaf.
    • Sepals 6, papery
    • Stamens 6
  • Fruit a berry, dry outside and jelly-like inside, containing 1 to 3 seeds.
  • Seed tan, narrowly oblong to obovate, 3mm-4mm


  • A waterside plant with iris-like leaves.
  • Distinguished from the Blue Flag Iris (Iris versicolor) with which it is often found by its decidedly unflower-like flower, and its brighter, yellow green color.
  • Distinguished from the introduced Eurasian Acorus calamus by having the midvein, plus 1 to 5 additional veins, more-or-less equally raised above leaf surface. (In Acorus calamus, only the midvein is prominently raised above leaf surface, the other veins scarcely raised if at all.)
  • Although leaf and spadix size of the two species overlap, those measurements differ significantly, with the Eurasian Acorus calamus tending to have longer and wider leaves and longer spadices.


  • Labrador and Quebec to Alaska, south to Virginia, Ohio, Iowa, Nebraska, Montana, northern Idaho, and Washington.
  • Specimens from central Siberia with similar leaf venation have been examined, and the species is perhaps holarctic in distribution.
  • In North America, Native Americans probably played a significant role in the present-day distribution of Acorus americanus because Sweet Flag rhizomes and plants were valued by many groups and were objects of trade. Disjunct populations occur in localities that are often near old Native American village sites or camping areas.


  • Edges of ponds and moist soils, marshes, shallow waters



  • Aromatic roots used medicinally and ritually by Algonquins, Cree and other NE tribes.
  • Acorus calamus, a sterile triploid, was introduced to North America by early European settlers, who grew it for medicinal uses. Rhizomes propagate easily, and the species has spread throughout northeast and central United States. Scattered populations occur elsewhere.


  • Long known for its medicinal value, and cultivated in Asia for this reason. Spicy-scented leaves and fragrant (but rather bitter-tasting) root often are used for sachets, medicines, and candy. Calamus root long was used in a home remedy for colic.
  • Oleum calami distilled from the rhizomes for use in perfumery and medicine.
  • Active ingredients: Asarone and beta-Asarone
  • The rhizomes, harvested in autumn or spring, are edible and can be used as a substitute for ginger, cinnamon or nutmeg; in the past were candied and used as a sweetmeat. The inner portion of young stems can be eaten raw and young leaves can be eaten cooked. Other virtues of this plant include its mature leaves, which are insect repellant, the lower stem and rhizome, which can be dried and used to scent clothes, cupboards etc, and an essential oil which can be extracted from the rhizome.
  • The rhizomes are considered to possess anti-spasmodic, carminative and anthelmintic properties and also used for the treatment of epilepsy, mental ailments, chronic diarrhoea, dysentery, bronchial catarrh, intermittent fevers and glandular and abdominal tumours. They are also employed for kidney and liver troubles, rheumatism, sinusitis, and eczema. It is also used as antibiotic and insecticide. (Whew!)
  • Leaves can be used as a substitute for vanilla pods. They can also be cut up and stored in dry foods to prevent infestation by weevils. Leaves and rhizomes are a nice addition to potpourri.
  • The rhizomes of Acorus calamus contain an aromatic oil that has been used medicinally since ancient times and has been harvested commercially. Native Americans exploited Acorus as a medicine and for ceremonial uses. Although this plant is cited in the ethnographic and ethnobotanical literature as Acorus calamus, the distribution of the tribes reported to use Acorus corresponds to the range of the native species.


  • Sexually by seed
  • Flowers June/July
  • Assexually by rhizome


  • By rhizome division


  • Hardy to USDA Zone 3 (average minimum annual temperature -40ºF)
  • Cultural Requirements
    • Full Sun
    • Permanently wet soil
  • Good for bogs and water gardens.
  • Available by mail order from specialty suppliers or occasionally at local nurseries. The related Asian species is available in a variegated form.



  • An unusual but appealing plant. A personal favorite.

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Last updated on 14 April, 2004