Proserpinaca palustris, the marsh mermaidweed or common mermaid-weed, is a species of flowering plant in the watermilfoil family (Haloragaceae). It is found in North America, the Caribbean, and Central America.
It has submerged leaves, which are sessile, 2- long. They are deeply divided into linear segments and the emergent leaves are simply serrated. It has fruits with concave sides and sharp or winged angles.[1]
There are two known varieties;P. palustris var. palustris - which has fruits 4-6mm wide, angles wing margined, very rare SE and NWP. palustris var. crebra (Fernald and Griscom) - which has fruits 2-4mm wide, angles not winged, occasional E and NW [1]
It grows in swamps, bogs, ponds and marshes.[1]