Northern Prairie Wildlife Research Center
2. Alisma plantago-aquatica L.
Some authors consider North American plants distinct from Old World A. plantago-aquatica. Old World examples have strongly pink or roseate petals rather than the essentially white petals of our plants. Although Old World A. plantago-aquatica has been reported as introduced to limited areas of North America, it has not been found in this region.
In separating American from European representatives, one or two species or varieties are commonly regarded to occur in this region. These include A. subcordatum Raf. and A. triviale Pursh, or considering these at the variety level, A. plantago-aquatica var. parviflora (Pursh) Farw. and var. americana Schultes & Schultes. Whether recognized at the species or the variety level, I find these entities are not clearly distinguishable among our material. They appear to be defined on character states that are intergradient and uncorrelated in populations of this region. North American plants may well deserve specific or varietal distinction relative to Old World counterparts, but there seems little if any basis for splitting within.