Alisma triviale Pursh
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Rhizome 1–2 cm thick; lvs usually long-petioled, the blade elliptic to broadly ovate, rounded to subcordate at base, 3–18 × 2–12 cm, 1.5–2.5(–2.7) times as long as wide; scape 1–10 dm; pedicels in whorls of 3–10; sep obtuse, 2–3 mm; pet white, 3.8–4.5 × 3.0–3.9 mm, half again as long as the sep; style short, 0.4–0.6 mm, the stigmatic part ± curved; achenes 15–23, 1.8–3.0 mm, ordinarily with a median dorsal groove, rarely with 2 grooves as in no. 3 [Alisma gramineum Lej.]; 2n=28. Marshes, ponds, and streams; N.S. and e. Que. to Pa., w. to s. B.C., Mo., N.M., and Calif. June–Sept. (A. brevipes; A. plantago-aquatica var. americanum)