Parrotfeather or Proserpinaca?

— Written By and last updated by
Parrotfeather (Myriophyllum aquaticum) is an aggressive non-native aquatic weed, most commonly found in the Piedmont and Coastal Plain. Extensive mats can form across lakes, ponds, swamps and along stream margins. The heavy growth of foliage and intertwined stems crowds out other vegetation, creating a monoculture that clogs waterways and reduces biodiversity. According to Invasive Exotic Plants of North Carolina (Cherri Smith/NC Department of Transportation), “Mechanical control tends to enhance its rate of spread and should only be conducted in small, contained waters.”  Chemical control is also quite difficult, but on the other hand failure to manage this weed does result in large scale degradation of surface waters. See the NC Agricultural Chemicals Manual for current aquatic weed control recommendations.
Parrotfeather morphology is highly distinctive, but it’s always possible to make an ID mistake, which can then result in damage to desirable native vegetation if a herbicide product is applied. One potential candidate for a false alarm is our native Proserpinaca palustris (mermaid weed).
Parrotfeather

Parrotfeather (Myriophyllum aquaticum) covering a large body of water near New Bern, NC, 12/27/20.

Proserpinaca palustris

Proserpinaca palustris, 12/27/20 at a different location. Foliage and growth habit superficially resemble parrotfeather, but parrotfeather creates a much denser vegetative cover.

Proserpinaca and Myriophyllum

Proserpinaca to the left, and Myriophyllum to the right. On closer view, substantial differences are
seen in the foliage. Proserpinaca leaves are alternately arranged on the stem; feathery, deeply cut Myriophyllum leaves are arranged in whorls of 3-6.

Leaves

Left to right: The feathery, deeply dissected leaf of Myriophyllum aquaticum; the typical dissected
leaf of Proserpinaca palustris; the typical serrate form of an emersed (above water) P. palustris leaf.