Disclaimer:

The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

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Common name: wandering hydrilla

Synonyms and Other Names: waterthyme

Identification: Submersed perennial herb. Rooted, with long stems that branch at the surface where growth becomes horizontal and dense mats form. Small, pointed leaves are arranged in whorls of 4 to 8. Leaves have serrated margins and may have one or more sharp teeth under the midrib (see Godfrey and Wooten 1979). Development of these features may vary with location, age, and water quality (Kay 1992).

The distribution of biotypes is changing rapidly (the monoecious biotype has spread south through Georgia, South Carolina, Tennessee, and Alabama). Populations north of South Carolina were often monoecious (having both male and female flowers on the same plant) (Cook and Lüönd 1982; Madeira et al. 2000). Fertile seed production was reported in the monoecious type (Langeland and Smith 1984). Both biotypes depend on tubers for overwintering, although monoecious hydrilla exhibits a more annual habit than the dioecious type, with abundant tuber/turion production around September (Owens et al. 2012).

Morphologically similar species include exotic Brazilian waterweed (Egeria densa), native western waterweed (Elodea nuttallii), and native (except Alaska and Puerto Rico) Canadian waterweed (Elodea canadensis). E. densa, E. nuttallii, and E. canadensis have 3-6 leaves per whorl, with inconspicuous leaf serration and no dentation on midrib, but E. densa leaves are 2-3 cm long, and both E. nuttallii and E. canadensis usually has 3 leaves per whorl near stem base (Langeland et al. 2008, Wunderlin and Hansen 2011, Rybicki et al. 2013).

Recent research into molecular techniques for identifying hydrilla and its biotypes has proven successful (Verkleij 1983; Ryan et al. 1995; Madeira et al. 2004). An early method used isoenzyme patterns in hydrilla to distinguish origin and biotype (Verkleij 1983). A later method used a random amplified polymorphic DNA (RAPD) procedure to find DNA markers in hydrilla samples (Ryan et al. 1995; Les et al. 1997; Madeira et al. 1997, 2000). A relatively inexpensive alternative method used “universal primers” to sequence hydrilla DNA (Madeira et al 2004; Benoit and Les 2013; Rybicki et al. 2013).

Size: Stems grow up to 9 m in length; leaves are 6-20 mm long and 2-4 mm wide.

Native Range: Korea appears the likely origin for the monoecious type (Madeira et al. 1997).

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Ecology: Hydrilla is found in freshwater lakes, ponds, rivers, impoundments, and canals. It mainly spreads vegetatively through dispersal of plant fragments, axillary turions, and tubers (Langeland and Sutton 1980). Tubers remain viable out of water for several days (Basiouny et al. 1978) and in undisturbed sediment for over 4 years (Van and Steward 1990). Viability remains after ingestion and regurgitation by waterfowl, although passage of vegetative propagules throught the digestive tract likely renders them non-viable (Joyce et al. 1980). Sexual reproduction among and between monoecious and dioecious strains is possible (Steward 1993), but its importance is unknown (Langeland and Smith 1984). Sites such as Lake Guntersville, Alabama have large co-occurring stands of monoecious and dioecious hydrilla. Pollination occurs when pollen from free-floating male flowers disperses on the water surface (epihydrophily) to female flowers (Tanaka 2000; Tanaka 2003). It has a low salinity tolerance (Carter et al 1987; Shields et al 2012).

Means of Introduction: The monoecious strain was a separate introduction, first found decades later in Delaware and the Potomac Basin (Environmental Laboratory 1985; Miller 1988; Madeira et al 2000).

Hydrilla is mainly introduced to new waters as fragments on recreational boats, their motors and trailers and in live wells. Stem pieces root in the substrate and develop into new colonies, commonly beginning near boat ramps. Once established, boat traffic continues to break and spread hydrilla throughout the waterbody. Both biotypes propagate primarily by stem fragmentation, although axillary buds (turions) and subterranean tubers are also important. Tubers are resistant to most control techniques (Schardt 1994) and may be viable as a source of reintroduction for years (Van and Steward 1990).

Hydrilla may be unknowingly transplanted into private ponds as a contaminant in water garden plants. It was found spreading after extensive 2,4-D use in Tennessee Valley Authority reservoirs and Lake Seminole, Georgia, once heavily populated with Eurasian water-milfoil (Myriophyllum spicatum) (Bates and Smith 1994). This has not yet been observed in northern lakes (M. Netherland, USACE pers. comm. 2015).

Status: Currently established in 18 states of the US (AL, CA, CT, DE, GA, IN, ME, MD, MA, NJ, NY, NC, OH, PA, SC, TN, VA, WV); occurrences in Washington, and Wisconsin were removed or controlled in isolated ponds (Herrera 2011; Asplund 2007).

Impact of Introduction:

Summary of species impacts derived from literature review. Click on an icon to find out more...

Ecological

It is commonly reported that once established, hydrilla results in an array of ecosystem disruptions. Hydrilla grows aggressively and competitively, spreading through shallower areas and forming thick mats in surface waters that block sunlight penetration to native plants below (van Dijk 1985). In the southeast, hydrilla effectively displaces beneficial native vegetation (Bates and Smith 1994) such as wild-celery (Vallisneria americana) and coontail (Ceratophyllum demersum) (van Dijk 1985; Rizzo et al. 1996). However, others reported that in a community of submerged aquatic vegetation including monoecious hydrilla, other exotic and native species responded to fluctuations in weather and water quality in the fresh tidal Potomac River (Carter et al. 1994) and the Upper James River in the Chesapeake Bay watershed (Shields et al. 2012). Hydrilla does not necessarily displace native species and may be beneficial to wildlife (Rybicki and Carter 2002; Rybicki and Landwehr 2007).

Hydrilla has been shown to alter the physical and chemical characteristics of lakes. Colle and Shireman (1980) found reduced weight and size in sportfish when hydrilla occupied the majority of the water column, suggesting that foraging efficiency was reduced as open water and natural vegetation gradients were lost. Stratification of the water column (Schmitz et al. 1993; Rizzo et al. 1996), decreased oxygen levels (Pesacreta 1988), and fish kills (Rizzo et al. 1996) have been documented in waters with hydrilla. Changes in water chemistry due to hydrilla may also be implicated in zooplankton and phytoplankton declines (Schmitz and Osborne 1984; Schmitz et al. 1993). However, other studies find a lack of negative effects of hydrilla on other biota, such as plants, fish, and aquatic bird communities (Killgore et al 1989; Hoyer et al 2008).

Dense beds of hydrilla affects water flow (Rybicki et al 1997) and water use. Beds in the Mobile Delta are reducing flow in small tidal streams and creating a backwater habitat (J. Zolcynski pers. comm. 1998). Its heavy growth may obstruct boating, swimming and fishing in lakes and rivers and may block the withdrawal of water used for power generation and agricultural irrigation. However, because of the resilience of hydrilla to control efforts and its competitive success and comparative vigor in stressed systems and capacity to provide at least some beneficial services combine to suggest it may have a useful role in some systems (Herschner and Havens 2008).

References: (click for full references)

Alabama Plant Atlas Editorial Committee. 2015. Alabama Plant Atlas. University of West Alabama, Livingston, AL. http://www.floraofalabama.org/.

Annear, S. 2008. Killer weed attacks pond. The Wicked Local Pembroke, Marshfield, MA. 2008 (November 7). http://www.wickedlocal.com/pembroke/news/x1772938647/Killer-weed-attacks-pond (accessed 10 November 2008).

Antillean group of Invasive Species (GAEI). 2015. Atlas de Especies Invasoras de Puerto Rico. University of Puerto Rico Agricultural Sciences, Mayagüez, PR.

Aquatic Control Technology. 2014. 2014 project completion report Long Pond, Mystic Lake, and Middle Pond – Barnstable, MA. Town of Barnstable, Barnstable, MA.

Ashe, D. and T. Driscoll. 2011. 2010 survey report - San Augustine City Lake. Texas Parks and Wildlife Department, Austin, TX.

Asplund, T. 2007. Hydrilla in Wisconsin. Aquatic Plant Management Society. Gainesville, FL. 2007 (86):6. http://apms.org/wp/wp-content/uploads/2012/10/086_oct2007.pdf.

Associated Press. 2009. Invasive Asian plant found in Kansas. Lawrence Journal-World. Lawrence, Kansas. http://www2.ljworld.com/news/2009/jul/28/invasive-asian-plant-found-kansas/. Created on 07/28/2009. Accessed on 08/05/2015.

Baker, J. 2002. Defending Massachusetts against biological invaders. http://www.mass.gov/czm/coastlines/2002/c33.htm.

Bates, A.L., and C.S. Smith. 1994. Submersed plant invasions and declines in the southeastern United States. Journal of Lake and Reservoir Management 10(1):53-55.

Basiouny, F.M., W.T. Haller, and L.A. Garrard. 1978. Survival of hydrilla (Hydrilla verticillata) plants and propagules after removal from the aquatic habitat. Weed Science. 26:502-504.

Bayne, D.R. 1979. The most troublesome aquatic weeds of Alabama. Proceedings of the Southern Weed Science Society 32:280-283.

Bellaud, M. 2010. Nor'Easter - a newsletter of the Northeast Aquatic Plant Management Society. Northeast Aquatic. Chester, NJ. 9 (2):6.

Benoit, L.K. and D.H. Les. 2013. Rapid identification and molecular characterization of phytoene desaturase mutations in fluridone-resistant hydrilla (Hydrilla verticillata). Weed Science 61:32-40.

Bernice Pauahi Bishop Museum. 2015. Bernice Pauahi Bishop Museum natual history data. Bernice Pauahi Bishop Museum, Honolulu, HI. http://nsdb.bishopmuseum.org/. Created on 04/03/2007. Accessed on 07/16/2015.

Bister, T.J. 2011. 2010 survey report - Lake Cypress Springs. Texas Parks and Wildlife Department, Austin, TX.

Carter, V., N.B. Rybicki, and C.L. Schulman. 1987. Effect of salinity and temperature on germination of monoecious hydrilla propagules. Journal of Aquatic Plant Management 25:54-57.

Carter, V., and N.B. Rybicki. 1994. Invasions and declines of submersed macrophytes in the tidal Potamac River and Estuary, the Currituck Sound-Back Bay system, and the Pamlico River Estuary. Journal of Lake and Reservoir Management 10(1):39-48.

Central Hardwoods Invasive Plant Network. 2010. Joint Aquatic Invasive Species Survey, 2010. University of Georgia, Athens, Georgia. http://www.rtrcwma.org/chip-n.

Colangelo, P.A. 1998. Fish and Boat Commission: Triploid Grass Carp Permit Applications. Pennsylvania Bulletin 28(40):4992.

Colle, D.E. and J.V. Shireman. 1980. Coefficients of condition for largemouth bass, bluegill, and redear sunfish in hydrilla-infested lakes. Transactions of the American Fisheries Society 109:521-531.

Cook, C.D.K. and R. Lüönd. 1982. A revision of the genus Hydrilla (Hydrocharitaceae). Aquatic Botany 13:485-504.

Cox, M.C., J.D. Madsen, and R.M. Wersal. 2010. Hydrilla and Giant salvinia survey in Mississippi for 2009. Geosystems Research Institute.

Driscoll, T. 2013. 2012 fisheries management survey report - Lake Timpson. Texas Parks and Wildlife Department, Austin, TX.

Ehrenfeld, J.G. 2003. Effects of exotic plant invasions on soil nutrient cycling processes. Ecosystems 6:503-523.

Environmental Laboratory. 1985. Monoecious Hydrilla in the Potomac River. Miscellaneous Paper MP A-85-5. US Army Engineer Waterways Experiment Station, Vicksburg, MS.

Erie-Times News Staff Report. 2015. Invasive species found in Pymatuning Lake. GoErie.com. Erie, PA. 06/12. http://www.goerie.com/article/20150612/GOCRAWFORD0103/306129999. Created on 06/12/2015. Accessed on 06/22/2015.

Falk, J. and T. Bryant. 1995. Purple loosestrife: a nuisance plant on the loose. Hydrilla: friend or foe? University of Delaware, Sea Grant College Program. Newark, DE. 1995 (Spring).

Findeisen, J. and G. Binion. 2014. 2013 fisheries management survey report - Dunlap Reservoir. Texas Parks and Wildlife Department, Austin, TX.

Foster, A., J. Boxrucker, G. Gilliland, and B. Wentroth. Updated by C. Tackett. 2009. Oklahoma aquatic nuisance species management plan. Oklahoma Department of Wildlife Conservation, Oklahoma City, OK.

Godfrey, R.K. and J.W. Wooten. 1979. Aquatic and Wetland Plants of Southeastern United States, Monocotyledons. University of Georgia, Athens, GA.

Gregory, P. 2009. State biologists confirm hydrilla infestation in Damariscotta Lake. Maine Department of Environmental Protection, Augusta, ME. Augusta, ME. Created on 09/24/2009.

Haller, W.T. 1982. Hydrilla goes to Washington. Aquatics 4(4):6-7.

Heineck, K. 2011. Boaters battle hydrilla at Claytor Lake. WSLS 10 News. 7 (27). http://www2.wsls.com/news/2011/jul/27/boaters-battle-hydrilla-claytor-lake-ar-1201320/.

Helton, R.J., and L.H. Hartmann. 1997. Statewide Aquatic Vegetation Survey Summary, 1996 Report. Inland Fisheries Division, Aquatic Habitat Enhancement, Jasper, Texas.

Herrera Environmental Consultants. 2011. Pipe and Lucerne Lakes - hydrilla and aquatic vegetation surveys 2010: final report. King County Department of Natural Resources and Parks, Olympia, WA.

Hershner, C., and K.J. Havens. 2008. Managing invasive aquatic plants in a changing system: strategic consideration of ecosystem services. Conservation Biology 22(3):544-550.

Hoyer, M.V., D.E. Canfield, C.A. Horsburgh, and K. Brown. 1996. Florida Freshwater Plants - A Handbook of Common Aquatic Plants in Florida Lakes. 1st edition. University of Florida IFAS Extension, Gainesville, FL.

Hoyer, M.V., M.W. Jackson, M.S. Allen, and D.E. Canfield II. 2008. Lack of exotic hydrilla infestation effects on plant, ?sh and aquatic bird community measures. Lake and Reservoir Management 24:331-338.

iMapInvasives. 2015. iMapInvasives New York. iMapInvaives. www.nyimapinvasives.org. Created on 07/08/2015. Accessed on 07/08/2015.

iNaturalist.org. 2015. iNaturalist research-grade observations. iNaturalist.org, San Francisco, CA. http://www.inaturalist.org/.

Johnson, B., and J. Manning. 1974. Hydrilla-the most serious threat to Louisiana water resources. Louisiana Conservationist 26:26-29.

Johnson, D.L. 1982. Hydrilla-a new aquatic weed in South Carolina. Palmetto Waters, South Carolina Water Resources Commission. Columbia, SC. 6 (8):1.

Johnson, J., R. Helton, L. Hartmann, and J. Cox. 1991. Weedy waters: foreign plants clog Texas waterways. Texas Parks and Wildlife 49(7):36-39.

Joyce, J.C., W.T. Haller, and D.E. Colle. 1980. Investigation of the presence and survivability of hydrilla propagules in waterfowl. Aquatics. 2:10-14.

Kansas Department of Wildlife, Parks and Tourism. 2009. Hydrilla eradication project underway at Olathe Pond. Kansas Department of Wildlife, Parks and Tourism. Topeka, KS. http://ksoutdoors.com/KDWPT-Info/News/News-Archive/2009-Weekly-News-Archive/7-15-09/HYDRILLA-ERADICATION-PROJECT-UNDERWAY-AT-OLATHE-POND. Created on 07/15/2009. Accessed on 08/05/2015.

Kay, S.H. 1992. Hydrilla: A Rapidly Spreading Aquatic Weed in North Carolina. North Carolina Cooperative Extension Service, North Carolina State University, Pub. AG-449, 11pp.

Kight, J. 1988. Tennessee-Tombigbee Waterway. Pages 324-329 in Proceedings of the 22th Annual Meeting on Aquatic Plant Control Research Programs. U.S. Army Corps of Engineers, Waterways Experiment Station. Vicksburg, MS.

King, M. 2008. Invasive water plant found in Sugar Loaf. Times Herald-Record, Middletown, NY. 2008 (October 4). http://www.recordonline.com/apps/pbcs.dll/article?AID=/20081004/NEWS/810040335/-1/NEWS14 (accessed 8 October 2008).

Kratville, D. 2013. The California Department of Food and Agriculture Hydrilla eradication program annual progress report 2013. California Department of Food and Agriculture, Sacramento, CA.

Langeland, K.A., and D.L. Sutton. 1980. Regrowth of Hydrilla from axillary buds. Journal of Aquatic Plant Management. 18:27-29.

Langeland, K.A., and C.B. Smith. 1984. Hydrilla produces viable seed in North Carolina lakes. Aquatics. 6:20-22.

Langeland, K.A., H.M. Cherry, C.M. McCormick, and K.A. Craddock Burks. 2008. Identification and Biology of Nonnative Plants in Florida's Natural Areas. 2nd Ed. UF IFAS Communication Services, Gainesville, FL.

Les, D.H., L.J. Merhoff, M.A. Cleland, and J.D. Gabel. 1997. Hydrilla verticillata (Hydrocharitaceae) in Connecticut. Journal of Aquatic Plant Management 35:10-14.

Louisiana Department of Wildlife and Fisheries, Inland Fish Division. 1998. Major public lakes of Louisiana with Hydrilla. Unpublished map prepared for in-office use.

Lynchburg News & Advance. 2010. APCo puts new guidelines in place to treat hydrilla at Smith Mountain Lake. WSLS 10. http://www2.wsls.com/sls/news/local/article/apco_puts_new_guidelines_in_place_to_treat_hydrilla_at_smith_mountain_lake/113727/.

Madeira, P., T. Van, D. Steward and R. Schnell. 1997. Random amplified polymorphic DNA analysis of the phenetic relationships among world-wide accessions of Hydrilla verticillata. Aquatic Botany 59:217-236.

Madeira, P.T., C.C. Jacono and T.K. Van. 2000. Monitoring hyrilla using two RAPD procedures and the Nonindigenous Aquatic Species Database. J. Aquat. Plant Manage. 38:33-40.

Madeira, P.T., T.K. Van, and T.D. Center. 2004. An improved molecular tool for distinguishing monoecious and dioecious Hydrilla. Journal of Aquatic Plant Management 42(1):28-32.

Madsen, J.D, R.M. Wersal, and W. Robles. 2006. Distribution of Hydrilla and Giant Salvinia in Mississippi in 2005. GeoResources Institute.

Madsen, J.D., G. Ervin, V. Maddox, & C. Abbott. 2010. Invasive Plant Atlas of the MidSouth. Mississippi State University. http://www.gri.msstate.edu/research/ipams/contactinfo.php.

Invasive Aquatic Species Program, Maine Department of Environmental Protection. 2015. Maine DEP 2015 Invasive Aquatic Plant Map. http://www.arcgis.com/home/webmap/viewer.html?webmap=126b9dbc59f44f969f74739bc9bc4ade&extent=-71.7106,43.2134,-68.6784,44.6356.

Manuel, K.L., J.P. Kirk, D.H. Barwick, and T.W. Bowen. 2015. Hydrilla management in Piedmont reservoirs using herbicides and triploid Grass Carp: A case study. North American Journal of Fisheries Management 33(3):488-492.

McConnell, J. 2010. No fast solution to hydrilla removal. Chesterfield Observer. August 11, 2010:4. http://www.chesterfieldobserver.com/news/2010-08-11/Front_Page/No_fast_solution_to_hydrilla_removal.html.

McFarland, D.G., and J.W. Barko. 1996. Investigations of the Production, Transport, and Survival of Monoecious Hydrilla Propagules in the Tidal Potomac River. US Army Engineer Waterways Experiment Station, Vicksburg, MS.

Miller, R.W. 1988. The First State's experiences controlling the northern monoecious form of hydrilla. Aquatics 10(2):16-23.

Montz, G.N. 1980. Distribution of selected aquatic plant species in Louisiana. Proceedings of the Louisiana Academy of Sciences 43:119-138.

Moore, K.A., D.J. Wilcox, and R.J. Orth. 2000. Analysis of the Abundance of Submersed Aquatic Vegetation Communities in the Chesapeake Bay. Estuaries 23(1):115-127.

National Park Service. 2012. NPSpecies - database of species inventories for park units in the National Park System. National Park Service, U.S. Department of the Interior. https://irma.nps.gov/App/Species/Welcome.

Netherland, M.D. 1997. Turion ecology of hydrilla. Journal of Aquatic Plant Management 35(1):1-10.

Netherland, M.D. and M. Greer. 2014. Establishing research and management priorities for monoecious hydrilla. APCRP Technical Notes Collection ERDC/TN APCRP-MI-8:12 pp.

North Carolina Division of Water Resources. 1996. Economical and Environmental Impacts of N.C. Aquatic Weed Infestations. North Carolina Department of Environment, Health, and Natural Resources, Raleigh, NC.

North Carolina State University Herbarium (NCSC). 2009. Herbarium Specimen Voucher Data, North Carolina State University, Raleigh, NC.

Northeast Aquatic Plant Management Society. 2009. Nor'Easter Newsletters. Northeast Aquatic Plant Management Society.

Orth, R.J., D.J. Wilcox, L.S. Nagey, J.R. Whiting, and J.R. Fishman. 2001. Distribution of submerged aquatic vegetation in Chesapeake Bay and coastal bays. Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, VA. http://web.vims.edu/bio/sav/sav00/index.html.

Oster, R., K. Frey, and P. Rister. 2008. Hydrilla observations in Kentucky. The Aquatic Plant Management Society, Vicksburg, MS. 2008 (89):3-4.

Ott Jr., R.A. and J.D. Norman. 2013. 2012 fisheries management survey report - Lake Jacksonville. Texas Parks and Wildlife Department, Austin, TX.

Owen, M. 2015. Dreaded aquatic plant returns to lakes. Ledger Enquirer. Columbus, GA. http://www.ledger-enquirer.com/news/local/article29464132.html. Created on 07/05/2015. Accessed on 07/06/2015.

Owens, C.S, R.M. Smart, and G.O. Dick. 2012. Tuber and turion dynamics in monoecious and dioecious hydrilla (Hydrilla verticillata). Journal of Aquatic Plant Management 50:58-62.

Parsons, J. 1996. Aquatic Plant Technical Assistance Program: 1995 Activity Report. Washington State Dept of Ecology, Environmental Investigations and Laboratory Services Program, Olympia, WA 98504-7710.

Pennsylvania Flora Database. 2011. Pennsylvania Flora Project. Morris Arboretum at the University of Pennsylvania (MOAR), Philadelphia, PA. http://www.paflora.org.

Pesacreta, G. 1988. Water Chemistry from North Carolina Piedmont Impoundments with Hydrilla (Hydrilla verticillata (L.f.)Royle). Ph.D. Dissertation, North Carolina State University, Raleigh, NC.

Rizzo, W.M., R.G. Boustany, and D.R. Meaux. 1996. Ecosystem changes in a subtropical Louisiana lake due to invasion by Hydrilla. Abstract in: From Small Streams to Big Rivers, Society of Wetland Scientists 17th Annual Meeting, June 9-14, 1996, Kansas City, MO.

Roach, H., J. Inabinet, and J. Tuten. 1993. Long term plan for aquatic plant management in Lake Marion and Lake Moultrie South Carolina. Santee Cooper, Environmental Resources Division, Monks Corner, SC.

Ruhl, H.A. and Rybicki, N. B. 2010. Long-term reductions in anthropogenic nutrients link to improvements in Chesapeake Bay habitat. Proceedings of the National Academy of Science 107(38):16566-16570.

Ryan, F.J., C.R. Cooley, and S.H. Kay. 1995. Coexistence of monoecious and dioecious hydrilla in Lake Gaston, North Carolina and Virginia. Journal of Aquatic Plant Management 33:8-12.

Rybicki, N.B., H.L. Jenter, V. Carter, and R.A. Baltzer. 1997. Observations of tidal flux between a submersed aquatic plant stand and the adjacent channel in the Potomac River near Washington, D.C. Limnology and Oceanography 42(2):307-317.

Rybicki, N.B. and V. Carter. 2002. Light and temperature effects on the growth of wild celery and hydrilla. Journal of Aquatic Plant Management 40(2):92-99.

Rybicki, N.B. and J.M. Landwehr. 2007. Long-term changes in abundance and diversity of macrophyte and waterfowl populations in an estuary with exotic macrophytes and improving water quality. Limnology and Oceanography 52(3):1195-1207.

Rybicki, N., J.D. Kirshtein, and M.A. Voytek. 2013. Molecular techniques to distinguish morphologically similar Hydrilla verticillata, Egeria densa, Elodea nuttallii, and Elodea canadensis. Journal of Aquatic Plant Management 51:94-102.

Sample, J. 1972. Hydrilla in Iowa. Weed Trees and Turf Cleveland, OH (October 1972):2.

Schardt, J. 1994. 1994 Florida Aquatic Plant Survey Report. Florida Department of Environmental Protection, Bureau of Aquatic Plant Management, Tallahassee, FL.

Schmitz, D.C. and J.A. Osborne. 1984. Zooplankton densities in a Hydrilla infested lake. Hydrobiologia 111:127-132.

Schmitz, D.C., B.V. Nelson, L.E. Nall, and J.D. Schardt. 1991. Exotic aquatic plants in Florida: a historical perspective and review of the present aquatic plant regulation program. Pages 303-326 in Center, T.C., R.F. Doren, R.L. Hofstetter, R.L. Myers, and L.D. Whiteaker, eds. Proceedings of a Symposium on Exotic Pest Plants. Technical Report NPS/NREVER/NRTR-91/06. National Park Service. Denver, CO.

Schmitz, D.J., J.D. Schardt, A.J. Leslie, F.A. Dray, Jr., J.A. Osborne, and B.V. Nelson. 1993. The Ecological Impact and Management History of Three Invasive Alien Aquatic Plant Species in Florida. Pages 173-194 in: B.N. McKnight (editor). Biological Pollution: The Control and Impact of Invasive Exotic Species. Indian Academy of Science, Indianapolis, IN.

SePRO Corporation, Aquatic Control, Aquatic Weed Control, and ReMetrix. 2015. 2014 Lake Manitou aquatic vegetation management plan update. Indiana Department of Natural Resources, Indianapolis, IN.

Shields, E.C., K.A. Moore, and D.B. Parrish. 2012. Influences of salinity and light availability on abundance and distribution of tidal freshwater and oligohaline submersed aquatic vegetation. Estuaries and Coasts 35:515-526.

Skrapits, E. 2015. New invasive plant found in Harveys Lake. citizensvoice.com. Wilkes-Barre, PA. http://citizensvoice.com/news/new-invasive-plant-found-in-harveys-lake-1.1826190. Created on 02/01/2015. Accessed on 08/12/2015.

Smithsonian National Museum of Natural History. 2015. Botany Collections. Smithsonian Institution, Washington, D.C. http://collections.nmnh.si.edu/search/botany/. Accessed on 07/09/2015.

South Carolina Department of Natural Resources. 2007. South Carolina Aquatic Plant Management Plan. South Carolina Department of Natural Resources.

Southern Company Generation Hydro Services. 2012. Bartletts Ferry hydroelectric project, FERC project number 485: volume 2, public, exhibit E. Georgia Power Company, Atlanta, GA. http://www.georgiapower.com/docs/about-energy/public-volume-2.pdf.

Steward, K.K., T.K. Van, V. Carter, and A.H. Pieterse. 1984. Hydrilla invades Washington, D.C. and the Potomac. American Journal of Botany 71(1):162-163.

Steward, K.K. 1993. Seed production in monoecious and dioecious populations of Hydrillla. Aquatic Botany. 46:169-183.

Stout, L. 2006. Hydrilla threat may grow: More lakes in northern Indiana could be closed. South Bend Tribune. 2006 (October 22). http://www.southbendtribune.com/apps/pbcs.dll/article?AID=/20061022 (accessed on October 31, 2006).

Tanaka, N. 2000. Pollination of the genus Hydrilla (Hydrocharitaceae) by waterborne pollen grains. Annals of the Tsukuba Botanical Garden 19:7-12.

Tanaka, N. 2003. Pollination of the genus Hydrilla (Hydrocharitaceae) by waterborne pollen grains: II. Air bubbles cause the male flower to surface. Annals of the Tsukuba Botanical Garden 22:143-145.

Tarbell, D. and Associates, Inc. 2007. Native and exotic submerged aquatic vegetation study. Appalachian Power Company, Roanoke, VA.

Tennessee Valley Authority. 1990. Final Environmental Assessment: Demonstration of use of grass carp in management of aquatic plants in Guntersville Reservoir. Tennessee Valley Authority, Water Resources Aquatic Biology Department, Muscle Shoals, AL.

Terlizzi, D.E. 1996. Toward regional management of aquatic nuisance species in the Chesapeake Bay Basin. Aquatic Nuisance Species Digest 1(4):38-47.

Texas Invasives. 2015. Texas Invasives Database. http://www.texasinvasives.org/.

Thomas, K.A., and P. Guertin. 2007. Southwest Exotic Mapping Program 2007: occurrence summary and maps of select invasive non-native plants in Arizona. US Geological Survey Open-File Report 2007-1277. http://pubs.usgs.gov/of/2007/1277/.

Thomas M. Pullen Herbarium. 2005. Thomas M. Pullen Herbarium. University of Mississippi, Oxford, MS. http://www.herbarium.olemiss.edu/. Accessed on 08/25/2015.

Thomaston, W.W. 1984. The status of undesirable aquatic weeds in Georgia during 1983. Aquatics 6(1):9-10.

U.S. Army Corps of Engineers (USACE). 2003. Aquatic Plant Management Plan for U.S. Army Corps of Engineers, Savannah District. U.S. Army Corps of Engineers, Savannah, GA.

U.S. Army Corps of Engineers (USACE). 2013. Invasive species profile system. US Army Corps of Engineers, Vicksburg, MS. http://corpslakes.usace.army.mil/employees/invasive/isps/index.cfm.

United States Department of Agriculture (USDA). 2008. PLANTS Database. National Plant Data Center. http://plants.usda.gov.

URS Corporation, Gomez and Sullivan Engineers, P.C. 2012. Final study report: water level management study - RSP 3.12. Exelon Generation Company, LLC, Chicago, IL.

Van, T. and K. Steward. 1990. Longevity of monoecious hydrilla propagules. J. Aquat. Plant Manage. 28:74-76.

van Dijk, G. 1985. Vallisneria and its interactions with other species. Aquatics 7(3):6-10.

Verkleij, J.A.C. 1983. A comparative study of the morphology and isoenzyme patterns of Hydrilla verticillata (L.f.) Royle. Aquatic Botany 17:43-59.

Walsh, S. 2010. Aquatic invasive species of Guam. USGS Southwest Biological Sciences Center, Gainesville, FL.

Wisconsin Department of Natural Resources (WI DNR). 2009. New invasive crayfish found in Wisconsin. Wisconsin Department of Natural Resources. Madison, WI. http://dnr.wi.gov/news/weekly/article/print.asp?id=1190. Created on 09/08/2009. Accessed on 09/02/2015.

Wunderlin, R.P., and B.F. Hansen. 2011. Guide to the Vascular Plants of Florida. 3rd Ed. University Press of Florida, Gainesville, FL.

Zolczynski, J., and R. Shearer. 1997. Mobile Delta Submersed Aquatic Vegetation Survey, 1994. Fisheries Section, Game and Fish Division, Department of Conservation and Natural Resources, Spanish Fort, AL.

Other Resources:
The Maine Invasion

Monoecious hydrilla literature review

Author: C.C. Jacono, M.M. Richerson, V. Howard Morgan, and I.A. Pfingsten

Peer Review Date: 10/27/2015

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.