1. Acorus calamus L. (sweet flag, calamus)

Pl. 26 a; Map 80

Plants perennial. Rhizomes relatively stout, sweetly scented. Leaves crowded basally, 1B2 m long, 10B25 mm wide, erect, linear, the midvein prominent and thickened, usually positioned slightly off-center. Inflorescences dense spikes (spadices) 3B10 cm long, 1B2 cm wide, the axis thickened, appearing lateral and sessile from the leaflike flowering stems (the inflorescence actually terminal and the long leaflike extension a modified bract called a spathe). Flowers tiny, perfect, actinomorphic. Tepals 6, yellowish brown. Stamens 6. Ovaries 1 per flower, superior, with 2 or 3 locules. Ovules 1 per locule. Fruits obpyramidal, dry, indehiscent, the sides somewhat sunken or shriveled, not producing mature seeds. 2n=36. MayBJuly.

Scattered nearly throughout the state (eastern U.S. and adjacent Canada west to South Dakota, Colorado, and Texas; also in California and Oregon). Various aquatic and semiaquatic habitats, including ditches, fens, prairie swales, spring branches, pond margins, and sloughs; usually emergent aquatics.

Acorus bears only a superficial resemblance to the genera of Araceae, with which it has long been associated (Grayum, 1987). The taxonomy of the genus has also been controversial. Wilson (1960) explained some of the reasons for maintaining A. americanus as a separate species native to the New World and restricting true A. calamus to plants native to the Old World. However, Thompson (1995) determined that all of the Missouri collections represent introduced populations of A. calamus, a sterile triploid that has been spread vegetatively by rhizomes, although these probably were spread long ago by waterfowl, European settlers, and perhaps Native Americans after the species was introduced in the northeastern United States (by the early nineteenth century). Acorus americanus has primarily a northern distribution but has been collected adjacent to Missouri in Iowa and Nebraska. It differs from A. calamus in having leaves with 2 to several prominent veins, instead of a single, thickened midrib. Unlike A. calamus, this fertile diploid (2n=24) produces fruit with viable seeds (Thompson, 1995).

Calamus root and its extracts have a long history of use as medicine, perfume additives, and food flavoring. The rootstocks are candied by boiling in sugar. The genus also was of religious significance to the Plains Indians.