Alisma subcordatum Raf.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Much like no. 1 [Alisma triviale Pursh], but with smaller fls; sep 1.5–2.3 mm; pet 1.8–2.5 × 1.4–2.0 mm, barely or scarcely longer than the sep; anthers 0.4–0.6 mm; style very short, 0.2–0.4 mm; achenes 1.5–2.2 mm; 2n=14. Usually in shallow water; Vt. and Mass. to N.D., s. to Fla. and Tex. (A. plantago-aquatica var. parviflorum) Variously reported to intergrade with no. 1 or to be genetically isolated from it.