Plants are submersed except the upper flower-bearing portions (unless
stranded at times of low water levels). The stem is thickened below the
inflorescence to almost double the width of the lower stem, characteristically
curved to lie parallel with the water surface. Leaves are whorled, sessile,
the submersed ones pinnately dissected into capillary segments. The bracteal
leaves or bracts subtending the flowers are reduced. The foliage leaves
have a grayish cast, the segments mostly disposed on the slender, commonly
branched stem in pairs, or subopposite, and whorled; the leaves with a
markedly feathery appearance; upper primary bracts of the inflorescence
less than 2.0 cm long, entire, obovate, lower bracts usually toothed,
sometimes entire; the lowermost flowers on the inflorescence usually female,
a few median ones bisexual, the upper male. The petals are 4, reddish
in the bisexual and male flowers, none in the female flowers.
Plants grow beneath the surface of the water, rooted in the substrate.
The upper flower-bearing portion of the stem is above the surface of the
water. Plants of this species never form turions but in colder climates
die back to the root crowns over winter. The species is rhizomatous, branches
freely and forms dense mats upon or near the surface of the water. Plants
root at the nodes; vegetative fragments may form new plants.
This species is known to occur in a variety of habits, becoming established
in both impoundments and natural waters, sometimes brackish water or in
clear, cool, spring-fed rivers.
Problems associated with this species include displacement of native
vegetation, disruption of navigation and recreation by the formation of
impenetrable mats, and decreased water flow.
The rapid growth rate of this species allows it to cover water surfaces
and displace native vegetation..