Hydrilla verticillata - (L. f.) Royle
Hydrilla
Other English Common Names: Water-thyme
Other Common Names: waterthyme
Taxonomic Status: Accepted
Related ITIS Name(s): Hydrilla verticillata (L. f.) Royle (TSN 38974)
Unique Identifier: ELEMENT_GLOBAL.2.159017
Element Code: PMHYD05010
Informal Taxonomy: Plants, Vascular - Flowering Plants - Other flowering plants
 
Kingdom Phylum Class Order Family Genus
Plantae Anthophyta Monocotyledoneae Hydrocharitales Hydrocharitaceae Hydrilla
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Concept Reference
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Concept Reference: Kartesz, J.T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland, OR.
Concept Reference Code: B94KAR01HQUS
Name Used in Concept Reference: Hydrilla verticillata
Conservation Status
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NatureServe Status

Global Status: GNR
Global Status Last Changed: 22Mar1994
Rounded Global Status: GNR - Not Yet Ranked
Nation: United States
National Status: NNA

U.S. & Canada State/Province Status
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United States Alabama (SNA), Arizona (SNA), California (SNA), Delaware (SNA), District of Columbia (SNA), Florida (SNA), Georgia (SNR), Kentucky (SNA), Louisiana (SNA), Maryland (SNA), New York (SNA), North Carolina (SNA), Pennsylvania (SNA), South Carolina (SNA), Tennessee (SNA), Texas (SNA), Virginia (SNA), Washington (SNA)

Other Statuses

NatureServe Global Conservation Status Factors

Other NatureServe Conservation Status Information

Distribution
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U.S. States and Canadian Provinces

Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
Color legend for Distribution Map
NOTE: The distribution shown may be incomplete, particularly for some rapidly spreading exotic species.

U.S. & Canada State/Province Distribution
United States ALexotic, AZexotic, CAexotic, DCexotic, DEexotic, FLexotic, GA, KYexotic, LAexotic, MDexotic, NCexotic, NYexotic, PAexotic, SCexotic, TNexotic, TXexotic, VAexotic, WAexotic

Range Map
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Ecology & Life History Not yet assessed
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Economic Attributes Not yet assessed
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Management Summary Not yet assessed
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Population/Occurrence Delineation Not yet assessed
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Population/Occurrence Viability
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U.S. Invasive Species Impact Rank (I-Rank)
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Disclaimer: While I-Rank information is available over NatureServe Explorer, NatureServe is not actively developing or maintaining these data. Species with I-RANKs do not represent a random sample of species exotic in the United States; available assessments may be biased toward those species with higher-than-average impact.

I-Rank: High/Medium
Rounded I-Rank: High
I-Rank Reasons Summary: This species has been called "the perfect aquatic weed" (Langeland 1997). Hydrilla verticillata alters ecosystem processes, community structure, and community composition by forming dense mats of floating vegetation that impede water flow and suppress all other aquatic vegetation (Langeland 1997, Batcher et al 2003, Jacono and Richerson 2003). It has a direct negative impact on several native plant species: Potamogeton spp., Vallisneria americana, and Ceratophyllum demersum (Ramey 2001). Numerous recent reports of new infestations in Pennsylvania, Massachusetts, Maine, New Jersey, Louisiana, California, Washington, and Arkansas (Jacono and Richerson 2003). Reproduces by propagules, known as "turions," and from plant fragments (Langeland 1997). Disperses by water currents, waterfowl, and human activity (Langeland 1997, Batcher et al 2003). Management is very difficult, requiring more than ten years (Langeland 1997, Balciunas et al. 2002, Batcher et al 2003).
Subrank I - Ecological Impact: High/Medium
Subrank II - Current Distribution/Abundance: Medium
Subrank III - Trend in Distribution/Abundance: High
Subrank IV - Management Difficulty: High
I-Rank Review Date: 23Feb2004
Evaluator: Heffernan, K.
Native anywhere in the U.S?
Native Range: Europe, Africa, India, Southeast Asia, Australia (Randall 2004)

Download "An Invasive Species Assessment Protocol: Evaluating Non-Native Plants for their Impact on Biodiversity". (PDF, 1.03MB)
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Screening Questions

S-1. Established outside cultivation as a non-native? YES
Comments: Streams, rivers, canals, lakes, ponds (Batcher et al 2003).

S-2. Present in conservation areas or other native species habitat? Yes
Comments: Natural freshwater habitats (Batcher et al 2003; Langeland 1997).

Subrank I - Ecological Impact: High/Medium

1. Impact on Ecosystem Processes and System-wide Parameters:High significance
Comments: Water flow; light and nutrient availability (Batcher et al 2003; Langeland 1997; Jacono and Richerson 2003).

2. Impact on Ecological Community Structure:High significance
Comments: Forms impenetrable mats on water surface (Batcher et al 2003; Langeland 1997; Jacono and Richerson 2003).

3. Impact on Ecological Community Composition:High significance
Comments: Suppressed all other aquatic species (Batcher et al 2003; Langeland 1997; Jacono and Richerson 2003).

4. Impact on Individual Native Plant or Animal Species:Low significance
Comments: Potamogeton spp., Vallismeria americana, Ceratophyllum demersum. (Ramey 2001).

5. Conservation Significance of the Communities and Native Species Threatened:Unknown
Comments: No data.

Subrank II. Current Distribution and Abundance: Medium

6. Current Range Size in Nation:High significance
Comments: Most of southeastern states from Virginia to Texas, California, Arizona, and Washington (Kartesz and Meacham 1999).

7. Proportion of Current Range Where the Species is Negatively Impacting Biodiversity:Low significance
Comments: Restricted to aquatic habitat (Batcher et al 2003; Langeland 1997; Jacono and Richerson 2003).

8. Proportion of Nation's Biogeographic Units Invaded:Moderate significance
Comments: Approximately ten TNC ecoregions invaded (Heffernan, pers. obs., using USDA-NRCS 2004; Slaats 1999).

9. Diversity of Habitats or Ecological Systems Invaded in Nation:High significance
Comments: Streams, rivers, ponds, lakes; a variety of nutrient regimes (Batcher et al 2003; Langeland 1997; Jacono and Richerson 2003).

Subrank III. Trend in Distribution and Abundance: High

10. Current Trend in Total Range within Nation:High significance
Comments: Numerous recent discoveries in Pennsylvania, Massachusettes, Maine, New Jersery, Louisana, California, Washington, and Arkansas (Jacono and Richerson 2003).

11. Proportion of Potential Range Currently Occupied:Low significance
Comments: Known from 690 waterbodies, 190 drainages, 21 states (Jacono and Richerson 2003).

12. Long-distance Dispersal Potential within Nation:High significance
Comments: Turions and stem fragments transported by water currents, boats, waterfowl (Batcher et al 2003; Langeland 1997).

13. Local Range Expansion or Change in Abundance:High significance
Comments: (Jacono and Richerson 2003).

14. Inherent Ability to Invade Conservation Areas and Other Native Species Habitats:High significance
Comments: High dispersal potential and establishes readily (Batcher et al 2003; Langeland 1997).

15. Similar Habitats Invaded Elsewhere:Unknown
Comments: Does occur as invasive elsehwhere, but no specific habitat information found that indicates uninvaded habitat here (PIER 2004).

16. Reproductive Characteristics:High significance
Comments: Sexual and vegetative reproduction; rapid growth (Batcher et al 2003; Langeland 1997).

Subrank IV. General Management Difficulty: High

17. General Management Difficulty:High significance
Comments: Aquatic habitat and vigorous reproductive capabilities (Balciunas et al. 2002; Batcher et al 2003; Langeland 1997).

18. Minimum Time Commitment:High significance
Comments: Many years of repeated treatments using herbicides (Balciunas et al. 2002; Batcher et al 2003; Langeland 1997).

19. Impacts of Management on Native Species:High significance
Comments: Herbicides used are contact poisons, copper sulfate and endothal, that are non-selective on plants and highly toxic to fish (Batcher et al. 2003).

20. Accessibility of Invaded Areas:Insignificant
Comments: Not identified as a difficulty.
Authors/Contributors
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Botanical data developed by NatureServe and its network of natural heritage programs (see Local Programs), The North Carolina Botanical Garden, and other contributors and cooperators (see Sources).

References
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  • Balciunas, J.K., M.J. Grodowitz, A.F. Cofrancesco, J.F. Shearer. 2002. Hydrilla. In: Van Driesche, R., et al., 2002. Biological Control of Invasive Plants in the Eastern United States, USDA Forest Service Publication FHTET-2002-04. Available: http://www.invasive.org/eastern/biocontrol/7Hydrilla.html (accessed 2004). 413 P.

  • Batcher, M.S., M. Tu, and B. Meyers-Rice. 2003. Element stewardship abstract: Hydrilla verticillata. The Nature Conservancy. Available at: http://tncweeds.ucdavis.edu/esadocs/documnts/hydrver.pdf (accessed February 2004). 10 p.

  • Flora of North America Editorial Committee. 2000. Flora of North America north of Mexico. Vol. 22. Magnoliophyta: Alismatidae, Arecidae, Commelinidae (in part), and Zingiberidae. Oxford Univ. Press, New York. xxiii + 352 pp.

  • Jacono, C.C. and M.M. Richerson. 2003. Hydrilla verticillata. United States Department of the Interior, Biological Resources Division, Center for Aquatic Resource Studies. Available at: http: nas.er.usgs.gov/plants/docs/hy_verti.html (accessed February 2004).

  • Kartesz, J.T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland, OR.

  • Kartesz, J.T. 1999. A synonymized checklist and atlas with biological attributes for the vascular flora of the United States, Canada, and Greenland. First edition. In: Kartesz, J.T., and C.A. Meacham. Synthesis of the North American Flora, Version 1.0. North Carolina Botanical Garden, Chapel Hill, N.C.

  • Langeland, K.A. 1997. Hydrilla verticillata: The perfect aquatic weed. University of Florida, Agronomy Department, Center for Aquatic Plants. Available at: http://aquat1.ifas.ufl.edu/hydcirc.html (accessed February 2004).

  • Pacific Island Ecosystems at Risk (PIER). 2004. Hydrilla verticillata. United States Department of Agriculture Forest Service Institute of Pacific Island Forestry. Available at http://www.hear.org/pier/species/hydrilla_verticillata.htm (accessed February 2004).

  • Ramey, V. 2001. Hydrilla verticillata. University of Florida, Center for Aquatic Plants. Available at http://plants.ifas.ufl.edu/seagrant/hydver2.html (accessed February 2004).

  • Randall, R. 2004. Global Compendium of Weeds. Department of Agriculture of Western Australia. Available at http://www.hear.org/gcw/index.html (accessed February 2004).

  • Slaats, J. 1999. TNC ecoregions and divisions map. Available at http://gis.tnc.org/data/MapbookWebsite/map_page.php?map_id=9 (accessed February 2004).

  • USDA, NRCS. 2004. The PLANTS Database, Version 3.5 (http://plants.usda.gov) . National Plant Data Center, Baton Rouge, LA 70874-4490 USA.

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