Hydrilla

Growth Form:  Forb

General:   Aquatic, herbaceous, submersed, perennial rooted in saturated soil, can grow in water a few inches deep to 20 feet deep.

Flowers:   Male and female: female flowers solitary, tiny, white, floating from stalk on water surface; male flowers tiny, greenish, attached to stems, until they break loose, rise to the surface and free-float.

Fruits and Seeds:   Reproduces mainly by regrowth of stem fragments, but also by buds at leaf nodes (turions, dark green, 1/4 inch round) and from 1/2 inch x 1/2 inch potato-like tubers (roots) below ground.

Leaves:   Green, 0.6 inches long, pointed tips, arranged in whorls of 3 to 10 joined directly to stem; whorls in long increments, 1/8 to 2 inches apart on stem. Leaf edges distinctly saw-toothed; plant noticeably rough when pulled through the hand.

Stems or Branches:   Submersed, slender and branching profusely across the water surface; up to 25 ft long. White roots grow from stem (adventitious roots).

Threatens:   Threatens any freshwater aquatic communities including springs, lakes, marshes, ditches, streams and rivers.

Look-Alikes:   Common Waterweed, Elodea canadensis; leaves occur in whorls of 3 around the stem (or opposite), without tubers. Non-native, Brazilian Waterweed, Egeria densa; leaves in whorls of 4 - 6 (8), bushier in appearance, without tubers.

Distribution:   Native to S. India and Korea. Known from Florida to Connecticut and west to California and Washington. Isolated populations found in Indiana (2007) and Wisconsin.

Other Links:  

http://plants.ifas.ufl.edu/seagrant/hydver2.html
http://www.invasivespeciesinfo.gov/aquatics/hydrilla.shtml
http://nas.er.usgs.gov/taxgroup/plants/docs/hy_verti.html
http://www.ecy.wa.gov/programs/wq/plants/weeds/aqua001.html