Publication: Sp. Pl. 1: 127. 1753 (as gramineum). 1753.
selected vouchers: WTU
Notes: FNA22: "Seven hybrids, Potamogeton gramineus Â´ P. nodosus (= P. Â´ argutulus Hagström), P. gramineus Â´ P. richardsonii (= P. hagstroemii A. Bennett [as hagstromii]), P. alpinus Â´ P. gramineus (= P. Â´ nericius Hagström), P. gramineus Â´ P. perfoliatus (= P. Â´ nitens Weber [P. Â´ subnitens Hagström]), P. gramineus Â´ P. natans (= P. Â´ sparganiifolius Laestadius ex Fries), P. gramineus Â´ P. illinoensis [= P. Â´ spathuliformis (J. W. Robbins) Morong)], and P. gramineus Â´ P. praelongus (= P. Â´ vilnensis Galinis), have been described.
Three varieties were recognized (E. C. Ogden 19435) and treated (M. L. Fernald 1950). These varieties, Potamogeton gramineus var. gramineus, deletion}P. gramineus var. myriophyllus, and P. gramineus var. maximus, were said to be separated by the shape and size of the submersed leaves. We have studied many populations of this species in the field and have observed on several occasions that a single population has leaf morphology variable enough to include all three varieties. We have, , therefore , chosen not to recognize any infraspecific categories for this species."
KZ99 mistakently places German P. heterophyllus as a synonym of New World P. illinoensis