New Flora and Botany of North America 1: 57. 1836.
Leaves basally white with pink or red, otherwise bright green; major veins 2–6, ± equally raised above leaf surface; cross section swollen in center, gradually tapering to ends. Vegetative leaves to 1.45 m; sheathing base (proximal part of leaf) 18.1–51.8(–58.8) cm; distal part of leaf 31.2–88.6(–100.4) × 0.3–1.2 cm, usually slightly longer to more than 2 times length of distal leaf, margins usually entire. Sympodial leaf (46–)56.8–148(–166.7) cm, usually equal to or slightly longer than vegetative leaves; sheathing base (20.9–)25.3–74.1(–100.2) cm; distal part of leaf (20.9–)27.9–77.9(–92.6) × 0.3–1.3 cm. Spadix 3.3–7.4(–8.7) cm × 4.7–10(–13.3) mm at anthesis; fruiting spadix 3.5–7.8(–8.8) cm × 6.9–18.2 mm. Flowers 2–3 mm; pollen grains usually deeply staining in aniline blue. Fruits obpyramidal, 4–6 mm. Seeds (1–)6(–14), tan, narrowly oblong to obovate, (2–)3–4 mm. 2n = 24.
Phenology: Flowering late spring–mid summer.
Habitat: Wet open areas, marshes, swales, and along edges of quiet water
Elevation: 0–900 m
Alta., B.C., Man., N.B., Nfld. and Labr. (Nfld.), N.W.T., N.S., Ont., P.E.I., Que., Sask., Alaska, Conn., D.C., Idaho, Ill., Ind., Iowa, Maine, Mass., Mich., Minn., Mont., Nebr., N.H., N.J., N.Y., N.Dak., Ohio, Pa., R.I., S.Dak., Vt., Va., Wash., Wis.
Acorus americanus, a fertile diploid, occurs from northeastern United States across Canada and the northern plains. Specimens from central Siberia with similar leaf venation were examined, and the species is perhaps holarctic in distribution. Examination of additional material is necessary to determine if northern Asian diploid plants are conspecific with A. americanus. In North America, Native Americans probably played a significant role in the present-day distribution of A. 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 (M. R. Gilmore 1931).
Acorus americanus is susceptible to infection by Uromyces sparganii (Uredinales).
Duvall, M. R., G. H. Learn Jr., L. E. Eguiarte, and M. T. Clegg. 1993. Phylogenetic analysis of rbcL sequences identifies Acorus calamus as the primal extant monocotyledon. Proc. Natl. Acad. Sci. U.S.A. 90: 4641--4644.