Chesapeake Bay Introduced Species Database


Acorus calamus

Common name(s):
Calamus
Asian Sweet Flag is a medicinal plant from Asia used for centuries as an expectorant and an anesthetic. It was brought to Europe in 16th century. It is a strange plant in that it doesn?t sexually reproduce as it's sterile with infertile flowers, but it does reproduce asexually by splitting its rhizomes (underground stems). In North America there is a similar species, also called Sweet Flag (Acorus americanus), that does sexually reproduce and is often confused with the sterile Asian plant. Because Asian Sweet Flag was such an important medicinal plant in Europe, it was introduced to North America very early; the first herbarium collection is from Philadelphia in 1824. It was found in Chesapeake Bay in the mid to late 1800s, and was likely both an intentional introduction as a garden plant and an unintentional one with dry ballast (rocks and dirt used for weight on sailing ships). In spite of its history as an important medicinal plant, it is no longer seen as economically valuable in our region.
Image courtesy of USDA Natural Resources Conservation Service.

Economic Impacts

Impact:
Acorus calamus (Calamus) was introduced as widely used medicinal plant, and confection (Fernald and Kinsey 1958), but currently has no economic importance as an herb in our region.

References- Fernald et al. 1958


Economic Impacts Outside Chesapeake Bay

Impact:
Acorus calamus (Calamus) was extensively used as a medicinal plant. Candied sweet-flag roots were also a popular confection, 'one of the few frivolities of our great-great-grandmothers' (Fernald et al. 1958).


Ecological Impacts

Impacts on Natives:
Competition
Our knowledge of impacts of Acorus calamus' (Calamus) invasion of the Chesapeake Bay region is hampered by the inability of most botanists to distinguish it from the native A. americanus. A. calamus now appears to be the predominant species of Acorus in the region (Thompson 1993). Most recent records of 'A. calamus' probably refer to the introduced species.

Competition- Replacement of the native Acorus americanus (Sweet-Flag) by A. calamus (Calamus) has apparently been widespread in heavily settled parts of the Eastern US and Canada, but larely unnoticed. In MD, all herbarium specimens examined (n=21, collected 1855-1973) were A. calamus. In VA, 2 specimens of A. americanus were found, the last collected in 1919, while 62 specimens of A. calamus were collected from 1892 to 1989 (Thompson 1995). Competition seems a likely cause for species replacement, but differential responses of species to human disturbance and environmental stresses have not been studied.

Food/Prey- Roots and seeds of both species of Acorus are important as food for muskrats and waterfowl (Thomas 1980; Thompson 1995). However, the effects of replacement of A. americanus by A. calamus have not been studied, to our knowledge.

References- Thomas 1980; Thompson 1995
Impacts on Non-natives:
Competition
Our knowledge of impacts of Acorus calamus' (Calamus) invasion of the Chesapeake Bay region is hampered by the inability of most botanists to distinguish it from the native A. americanus. A. calamus now appears to be the predominant species of Acorus in the region (Thompson 1995). Most recent records of 'A. calamus' probably refer to the introduced species.

Competition- Competitive interactions between Acorus calamus (Calamus) and Iris pseudacorus (Yellow Iris) were studied by Thomas (1980) in marshes on Theodore Roosevelt Island in the Potomac River. Thomas was apparently unaware of the distinction between A. calamus and A. americanus, but based on Thompson's survey of herbarium specimens, these plants were probably true A. calamus. Acorus sp. is expected to succeed I. pseudacorus in many areas of the marsh, but the iris is favored by debris and disturbance, and so is likely to remain on the island in swamp transition area (Thomas 1980).

References- Thomas 1980; Thompson 1993


This data was last modified on Friday, September 9th, 2005.
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