Field Marks: The distinguishing features of this aquatic plant are its whorled leaves and its
flowers borne in the axils of ordinary leaves.
Habitat: Shallow water.
Habit: Aquatic perennial, often with a reddish hue.
Stems: Much branched, sometimes reddish, smooth, stout, bearing many leaves.
Leaves: Whorled, up to 2 1/2 inches long, with 10-25 thread-like segments on each side, smooth.
Flowers: Male and female flowers borne separately and on different plants in the axils of ordinary leaves on emergent inflorescences; each flower subtended by a 2- or 3-cleft, thread-like bracteole.
Sepals: 0.
Petals: Usually 0.
Stamens: 4.
Pistils: Ovary superior, 4-lobed, smooth.
Fruits: Nearly spherical, smooth, up to 1/8 inch in diameter, with a granular texture.
Notes: This aquatic may become an aggressive weed in shallow bodies of water. It is a popular aquarium plant. In North America, apparently only female plants occur. This species is called M. aquaticum by Gleason and Cronquist, Godfrey and Wooten, and most other recent authors.