Acorus americanus

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. However, Kartesz (5/98 review draft dataset) considers both A. calamus (in this strict sense) and A. americanus to be native to the United States and Canada.

Acorus americanus is a perennial herb occurring at the margins of still waters, within marshes, shallow depressions, calcareous seeps, and other open, damp habitats of the northeastern United States across Canada and the northern plains. It is an important medicinal plant for many Native American tribes, and it was traded and cultivated along trade-routes. There are 400 estimated occurrences of this species, which are threatened by over-harvest, development, water diversion, alteration of hydrology, erosion, succession, recreational activities, invasive species, drought, and other threats in some places. With a large range extent, high number of occurrences, abundant habitat, broad habitat preferences, and no obvious intrinsic vulnerabilities, this species is considered secure.

Acorus americanus occurs in northern North American from Alaska and the Northwest Territories south to Idaho, east to Maryland, and north to Newfoundland and Labrador in the in the United States and Canada (FNA 2000, Weakley and the Southeastern Flora Team 2024). Weakley and the Southeastern Flora Team (2024) note "because this species has not generally been recognized in floras, its distribution is poorly known; additional distributional records should be expected and sought." Range extent was estimated to be over 5 million square kilometers using herbarium specimens and photo-based observations documented between 1993 and 2024 (GBIF 2024, iNaturalist 2024, SEINet 2024).

By applying a 1 km separation distance to herbarium records and photo-based observations documented between 1993 and 2024, there are estimated to be over 400 occurrences rangewide (GBIF 2024, iNaturalist 2024, SEINet 2024).

Although threats are not widely documented, Acorus americanus is potentially threatened by over-harvest, development, water diversion, alteration of hydrology, erosion, succession, recreational activities, invasive species, drought, and other threats in some places, though there is insufficient data, including anecdotal accounts, to understand scope and severity of threats for this species.