Potamogeton perfoliatus is close relative of Potamogeton praelongus, but differs from the latter in its rhizomes unspotted (vs. spotted rusty-red), leaves ovate or ovate-oblong to lanceolate (vs. linear-lanceolate to ovate-oblong), minutely denticulate (vs. entire), apex flat, not splitting when pressed (vs. cucullate and splitting when pressed), stipules 3-22 mm (vs. 10-88 mm).
