Many similarities to : other Milfoils such as Spiked Water-Milfoil (Myriophyllum spicatum),, Alternate Water-Milfoil (Myriophyllum alterniflorum), Parrot's Feather (Myriophyllum aquaticum), Two-leaf Water-milfoil (Myriophyllum heterophyllum) nor with Red Water-milfoil (Myriophyllum verrucosum).
The leaves of the related Spiked Water-Milfoil are between 0.5 to 1.5 times as long as are the gaps between the whorls on the stem and each has between 13 to 35 segments (whereas those of Whorled Water-milfoil are between 1.5 to 4 times longer than the (shorter) internodes between whorls, 25 to 35 segments). The flower spike of Spike Water-milfoils do not collapse when removed from the water (whereas those of Whorled Water-milfoil do). Also, the leaves of Spiked Water-Milfoil are all below the waters surface, whereas the leaves of Whorled Water-milfoil are intermingled between the flowers and above water-level (although there are also submerged leaves without intermingled flowers).
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