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Hydrilla Identification

hydrilla-stem-and-whorl-low-michael-j-grodowitz-u-s-army-engineer-research-and-dvlpmnt-cntr

    Michael J. Grodowitz U.S.A.C.E.

Habit

  • Hydrilla is a herbaceous perennial.
  • Submersed, “obligate” (requiring a wet habitat).
  • Forming dense stands of very long stems (25 ft.) in the water.
  • Reproduces mainly by regrowth of stem fragments; also reproduces by growth of axillary buds(turions) and subterranean tubers; tubers can remain viable for more than 4 years (Van & Steward 1990).
  • A single tuber can grow to produce more than 6,000 new tubers per m2 (Sutton et al. 1992).

cbg-hydrilla-id-sheet-high-res-back-with-just-the-tuber-photos-shown

Hydrilla tubers look like pinto beans and can lead to new infestation.

 

Habitat

  • Hydrilla can grow in almost any freshwater: springs, lakes, marshes, ditches, rivers, tidal zones.
  • Can grow in only a few inches of water, or in water more than 20 feet deep.
  • Can grow in oligotrophic (low nutrient) to eutrophic (high nutrient) conditions.
  • Can grow in 7% salinity of seawater (Haller 1974).
  • Temperature tolerance: hydrilla is somewhat winter-hardy; its optimum growth temperature, 20-27o C (68-81o F); its maximum temperature, 30o C (86o F) (Kasselmann 1995).
  • U.S. southern populations overwinter as perennials; northern populations overwinter and regrow from tubers.
  • Can grow in only 1% of full sunlight.
  • Low light compensation and saturation points and low CO2 compensation point make it a competitive plant because it can start growing in low light before other plants do (Van et al. 1976; Bowes 1977).
niipp-hydrilla-2
Infested pond – Northeastern Illinois Invasive Plant Partnership


Origin

  • There is only one species of Hydrilla in the world.
  • Hydrilla verticillata’s dioecious type (plants having female flowers only) originates from southern India. Hydrilla’s monoecious type (plants having male and female flowers on the same plant) is probably from
    Korea. (Madeira et al. 1997).
  • Occurs in Europe, Asia, Australia and the Pacific, Africa, South America and North America.

                                        robert-videki-2robert-videki

Photo courtesy Robert Vidéki, Bugwood.org
 Leaves grow in whorls and have noticeably toothed edges.

 


cbg-hydrilla-id-sheet-high-res-front-with-just-the-id-portionBrazilian Elodea and American Elodea are two Hydrilla look-a-likes.

Just remember that Hydrilla grows in whorls of 3 or more, has noticeably toothed edges, and is the only plant to produce tubers

Additional resources

Travels with Hydrilla – Chessapeake Quartely, 2009

Why Hydrilla is Bad California Department of Food and Agriculture, 2015