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Invasive Freshwater Plants and Algae


  • Scientific Name

    Hydrilla verticillata - Visit ITIS for full scientific classification. 

  • Description


    • Submerged waterweed forms dense mats.
    • Has long stems, single white flowers (3 petals) at water surface.
    • Leaves are smooth and narrow, with teeth on edges and no stalks, placed in groups along stems.
    • Looks like Egeria except that upper and middle leaves are 1/4" - 3/4" long.
    • Often has 5 leaves per group.
    • The similar Elodea often has 3 leaves per group. 
  • Habitat
    • Still or slow-moving, freshwater habitats with high nutrient levels.
    • Tolerates low light, low salinity, turbidity and pollution.
    • Can survive near freezing temperature.
  • Invasion Pathways and Distribution
    • Native to warm areas of Asia (and maybe central Africa).
    • Now occurs in tropical and temperate areas worldwide.
    • It has been eradicated in many areas of California but still occurs in many other areas. 
  • Life History
    • In U.S. plants may produce pollen and seed bearing flowers or only seed bearing flowers.
    • Can grow and infest from pieces.
    • Special tubers overwinter in mud and stems form special overwintering buds called turions. 
  • Impacts
    • Aggressively invades new areas, displacing other plants and changing aquatic ecosystems.
    • Forms dense, submerged mats that reduce water flow, interfere with boating and fishing, and clog pumps needed for irrigation, water supply, and flood control. 
  • References and Useful Links

    For references by category and links to other useful AIS sites see our LEARN MORE page.