Acorus calamus

As treated by Kartesz, Acorus calamus excludes the plants sometimes treated as Acorus calamus var. americanus, which (following Thompson, 1995, Ph.D. diss., U.Illinois) is treated by him as Acorus americanus. Kartesz (1999) considers at least some material of both species to be native in North America. LEM 8Jun98 & 14Jun99. There has been confusion or disagreement as to the native status of this species in North America (Gleason and Cronquist 1963, Great Plains Flora Association 1986, Hitchcock and Cronquist 1976). Kartesz (1999) now recognizes two species (sometimes treated by others as varieties) of Acorus in North America. Under this taxonomy, Acorus americanus is the name given the native North American taxon, while A. calamus refers to the primarily Eurasian taxon, which is also considered native in parts of its present range in North America. Most botanists also consider these two taxa separate; however, there remains a great deal of disagreement about whether A. calamus is native anywhere in North America or not. The two are superficially very similar and difficult to distinguish, but they differ in chromosome number as well as other important characteristics (Michael Oldham pers. comm.). A commonly cited morphological difference between these taxa is the presence of only one raised vein running the length of the basal leaves in the Eurasian taxon, whereas the native North American taxon has two or more such veins (Swink and Wilhelm 1994). As further evidence that these taxa are not conspecific, one herbal remedy guide reports that the Eurasian material contains a carcinogen which North American material lacks (Tierra 1990). Packer and Ringius (1984) contains information regarding the taxonomic status and distribution of Acorus in Canada. There remains a great deal of confusion and disagreement among botanists regarding this species. Many reports of Acorus calamus throughout North America probably belong to A. americanus instead.

It is likely that this species is in rangewide decline due to the disappearance and degradation of its wetland habitats. The recent splitting of Acorus at the species level means that it is uncertain for many occurrences whether they are A. calamus or A. americanus. When this is sorted out it may become evident that one species is rarer or more common than originally thought.

Please see Kartesz (1999) for the updated global range information for Acorus calamus and A. americanus. In North America, A. calamus is mostly concentrated in plains and eastern locations. This species is also reported from Eurasia in the former Soviet Union (Hulten, 1968; Gleason and Cronquist 1963). A. calamus is reported to occur throughout most of the eastern U.S. except Florida, and also in Washington, Oregon, California, South Dakota, Nebraska, Kansas, Oklahoma, and Texas (Kartesz 1999). It is considered an exotic in Ontario (Ontario Natural Heritage Information Centre), Nebraska (Nebraska Natural Heritage Program), Missouri (Missouri Department of Conservation), and Kansas (Kansas Natural Features Inventory). It is historical in Delaware (Delaware Natural Heritage Program) and in Colorado. The Missouri populations were reportedly introduced by settlers for medicinal use (Tim Smith pers. comm.). It is known from seven counties in South Dakota (South Dakota Natural Heritage Database). It is reported from southern lower Michigan (Michigan Natural Features Inventory). It is reported from all counties in Maine (Maine Natural Areas Program).

Packer and Ringius (1984) contains information regarding the taxonomic status and distribution of Acorus in Canada. Only Acorus americanus (A. calamus var. americanus) occurs in Manitoba (Manitoba Conservation Data Centre).

At least a few hundred North American occurrences for this species known, at least some of which may be native as well as a sizable Eurasian range (cf. Hulten, 1968). "Uncommon" in California (Hickman 1993). There is one population reported from Alaska (Hulten 1968). It is reported to be "not very common" in Nebraska (Nebraska Natural Heritage Program). It is reported to be "common" in Maine (Maine Natural Areas Program). The plant is not rare in New Hampshire (New Hampshire Natural Heritage Inventory). Fourteen occurrences are reported from seven counties in South Dakota (South Dakota Natural Heritage Database). Roughly one hundred occurrences of Acorus are reported from Ontario, including occurrences of both A. calamus and A. americanus (Ontario Natural Heritage Information Centre). Five populations are reported from the Okeefenokee Swamp in southern Georgia, but the taxonomic status of these occurrences is uncertain. Both taxa are genuinely rare in Georgia (Georgia Natural Heritage Program). It is infrequent in marshes, on pond margins, along streams, and in ditches throughout the state of Kentucky (Kentucky Natural Heritage Program). It is reported as common in wetlands across the state of New York (New York Natural Heritage Program). Acorus is common in Indiana in wet fields, ditches, and marshes, but the Indiana NHP has not tried to distinguish the two species of Acorus, and their relative abundance in the state is unknown (Indiana Natural Heritage Data Center). 40 to 50 occurrences are reported from Kansas (Kansas Natural Features Inventory). One occurrence is documented by the Mississippi Natural Heritage Program for the state (Mississippi Natural Heritage Program). A. calamus is rare in Texas with a few wetland occurrences known from the northeastern corner of the state (Texas Natural Heritage Program). It is known historically from three populations in Colorado, all of which appear to have been extirpated. Worldwide, there are probably many thousands of populations.

An individual with the U.S. herbal medicinal industry states that trade in the plant is modest, on the order of 2000-3000 pounds per year, and that it is the root that is used (McGuffin pers. comm.).

In northeastern South Dakota, the Dakota tribe collects and utilizes an unknown quantity of this plant (David Ode pers. comm.). It is reportedly collected in Canada and the northeastern U.S. for sale on the herb market (Robyn Klein pers. comm.).

Acorus calamus is listed by the United Plant Savers At Risk Forum on their "To Watch" list. This list consists of "herbs which are broadly used in commerce and which, due to over-harvest, loss of habitat, or by the nature of their innate rareness or sensitivity are either at risk or have significantly declined in numbers within their current range." (United Plant Savers 2000)

With the general disappearance and degradation of wetlands, the habitat of this species continues to shrink. Because it is associated with relatively undisturbed habitats when compared with Acorus calamus, A. americanus is probably more threatened in some parts of its range as more undisturbed wetlands become disturbed. Replacement of A. americanus by A. calamus is possible as more wetland habitats become disturbed where the two species overlap. Channelization of springruns has been implicated as a threat to occurrences of this species in Georgia (Tom Patrick pers. comm.). Urban sprawl is causing widespread degradation of potential habitat for this species in southern Lower Michigan (Mike Penskar pers. comm.). Lack of monitoring resources available to properly document the population trends for this species are cited as a threat in Mississippi (Mississippi Natural Heritage Program).