Ludwigia grandiflora - (M. Micheli) Greuter & Burdet
Large-flower Primrose-willow
Other English Common Names: Large-flower Seedbox, Uruguay Seedbox
Other Common Names: large-flower primrose-willow
Synonym(s): Ludwigia uruguayensis (Camb.) Hara
Taxonomic Status: Accepted
Related ITIS Name(s): Ludwigia uruguayensis (Camb.) Hara (TSN 27365)
Unique Identifier: ELEMENT_GLOBAL.2.141235
Element Code: PDONA0B0U0
Informal Taxonomy: Plants, Vascular - Flowering Plants - Evening-Primrose Family
 
Kingdom Phylum Class Order Family Genus
Plantae Anthophyta Dicotyledoneae Myrtales Onagraceae Ludwigia
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Concept Reference
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Concept Reference: 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.
Concept Reference Code: B99KAR01HQUS
Name Used in Concept Reference: Ludwigia grandiflora
Taxonomic Comments: Ludwigia grandiflora was recently (Zardini et al., 1991; 1992) delineated as a distinct species from the Ludwigia uruguanyensis species complex. Ludwigia hexapetala was also similarly delineated but has since been synonymized with Ludwigia grandiflora.
Conservation Status
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NatureServe Status

Global Status: GU
Global Status Last Reviewed: 03Apr2006
Global Status Last Changed: 03Apr2006
Rounded Global Status: GU - Unrankable
Reasons: There is some uncertainty over the native range of Ludwigia grandiflora.
Nation: United States
National Status: NNR

U.S. & Canada State/Province Status
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.
United States Alabama (SNR), Arkansas (SNR), California (SNR), District of Columbia (SH), Florida (SNR), Georgia (S4?), Kentucky (SNR), Louisiana (SNR), Mississippi (SNR), Missouri (SNR), New Jersey (SNA), New York (SNA), North Carolina (S3), Oklahoma (SNR), Oregon (SNR), Pennsylvania (SNR), South Carolina (SNR), Tennessee (SNR), Texas (SNR), Virginia (SNA), Washington (SNR), West Virginia (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 AL, AR, CA, DC, FL, GAnative and exotic, KY, LA, MO, MS, NC, NJexotic, NYexotic, OK, OR, PA, SC, TN, TX, VAexotic, WA, WVexotic

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
Rounded I-Rank: High
I-Rank Reasons Summary: This species is considered a nuisance plant throughout most of its invaded range and forms dense stands that eliminate native vegetation by forming monospecific stands that competitively exclude other flora. It also eliminates open-water habitats that are important foraging-grounds for birds and other wildlife including rare fish and invertebrates. Large plant biomass results in a reduction in dissolved oxygen, an increase in acidity of the water, the eutrophication of the water body, and an increase in sedimentation. The species continues to spread aggressively in the Gulf and southeastern states and the western states including into undisturbed areas as the plant is easily dispersed and reproduces rapidly and aggressively. No management method is known to effect successful long-term control and management impacts on native species are high.
Subrank I - Ecological Impact: High/Medium
Subrank II - Current Distribution/Abundance: High
Subrank III - Trend in Distribution/Abundance: High
Subrank IV - Management Difficulty: High/Medium
I-Rank Review Date: 27Jun2006
Evaluator: J. Cordeiro, rev. K. Gravuer
Native anywhere in the U.S?
Native Range: Global range includes two disjunct areas, one in southern Brazil, Bolivia, northeastern Argentina, Uruguay, and Paraguay (also locally in Guatemala), and the second (with relevance here) in the southeastern United States coastal plains of southern South Carolina, Georgia, northern Florida, and Louisiana, west to central Texas; and once in southwest Missouri (Zardini et al., 1991; Crow and Hellquist, 2000a).

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Screening Questions

S-1. Established outside cultivation as a non-native? YES
Comments: In the southeastern and Gulf portions of the United States, water primrose has been considered a nuisance plant in most of its range (Benson et al., 2001; Chester and Holt, 1990; McGregor et al., 1996; Washington State Noxious Weed Control Board, 2006); as well as in some parts of California where it is locally common and Washington where it can dominate ditch margins in the Longview/Kelso Diking District in Cowlitz County (Washington State Noxious Weed Control Board, 2006; Zardini et al., 1991). Although there is some question as to whether is naturalized or native in the southestern United States, it has certainly invaded portions of this region and is an established invasive in the northeast and Pacific northwest.

S-2. Present in conservation areas or other native species habitat? Yes
Comments: In the southeastern and Gulf portions of the United States, water primrose has been considered a nuisance plant in most of its range (Benson et al., 2001; Chester and Holt, 1990; McGregor et al., 1996; Washington State Noxious Weed Control Board, 2006); as well as in some parts of California where it is locally common and Washington where it can dominate ditch margins in the Longview/Kelso Diking District in Cowlitz County (Washington State Noxious Weed Control Board, 2006; Zardini et al., 1991). Although there is some question as to whether is naturalized or native in the southestern United States, it has certainly invaded portions of this region and is an established invasive in the northeast and Pacific northwest.

Subrank I - Ecological Impact: High/Medium

1. Impact on Ecosystem Processes and System-wide Parameters:High/Moderate significance
Comments: Large plant biomass results in a reduction in dissolved oxygen, an increase in acidity of the water, the euthrophication of the water body, and an increase in sedimentation (Dutartre, 2004; Wittenberg, 2005). Mats impair water flow and has the potential to dominate shoreline vegetation if introduced to lakes, rivers, ponds, ditches, or streams (Washington State Noxious Weed Control Board, 2006). In Laguna, California, Ludwigia may also contribute to flooding in the Laguna system, as plant biomass fills in flood control channels, reducing its capacity for flood-retention and altering the characteristics of the wetland. Perennial Ludwigia mats slow the movement of water through the system, trapping trash and debris and likely fine sediments, further reducing flood-storage capacity and degrading the wetland. Over the long term, with no remediation, Ludwigia will potentially lead to a decrease in shallow wetland areas overall, but with increased flooding during storm events (Sonoma County Water Agency, 2005).

2. Impact on Ecological Community Structure:High significance
Comments: Ludwigia grandiflora forms dense stands that eliminate native vegetation by forming monospecific stands that competitively exclude other flora (Wittenberg, 2005).

3. Impact on Ecological Community Composition:High/Moderate significance
Comments: Ludwigia grandiflora forms dense stands that eliminate native vegetation by forming monospecific stands that competitively exclude other flora (Wittenberg, 2005). Mats impair water flow and has the potential to dominate shoreline vegetation if introduced to lakes, rivers, ponds, ditches, or streams (Washington State Noxious Weed Control Board, 2006). Recent expansions in California have prompted the California Invasive Plant Council to rate Ludwigia as a High Impact invasive species due to its ability to rapidly invade unexploited ecosystems (Sonoma County Water Agency, 2005); and it is also listed as a noxious weed in Washington, Florida, North Carolina, and South Carolina.

4. Impact on Individual Native Plant or Animal Species:Medium/Low significance
Comments: Ludwigia grandiflora forms dense stands that eliminate native vegetation by forming monospecific stands that competitively exclude other flora. Dense mats can also reduce the habitat of surface water birds (Wittenberg, 2005). In France, it has been found to compete with native plants (Dutartre, 2004). Similarly, evidence suggests Ludwigia hexapetala (here considered a synonym) outcompetes native wetland species in the Laguna de Santa Rosa, California. Ludwigia is also a direct threat to the diversity of native plant and animal communities, growing over surrounding vegetation to produce a thick mat of woody perennial stems and decaying plant matter. This mat inhibits the recovery and recruitment of other plants, and eliminates open-water habitats that are important foraging-grounds for birds and other wildlife. As Ludwigia tissue sloughs off or dies back and decomposes, microbial growth reduces dissolved oxygen in the water, impacting fish and invertebrate populations. Eighteen species of fish are found in the Laguna, including threatened populations of steelhead that use Laguna channels for seasonal passage to upstream breeding habitats. Current efforts to protect and enhance wetland habitats for migratory birds and waterfowl on the Pacific Flyway are substantially limited by Ludwigia growth, especially in the CDFG's Laguna Wildlife Area, site of the proposed Ludwigia control project (Sonoma County Water Agency, 2005).

5. Conservation Significance of the Communities and Native Species Threatened:Medium/Low significance
Comments: Ludwigia is also a direct threat to the diversity of native plant and animal communities, growing over surrounding vegetation to produce a thick mat of woody perennial stems and decaying plant matter. This mat inhibits the recovery and recruitment of other plants, and eliminates open-water habitats that are important foraging-grounds for birds and other wildlife. As Ludwigia tissue sloughs off or dies back and decomposes, microbial growth reduces dissolved oxygen in the water, impacting fish and invertebrate populations. Eighteen species of fish are found in the Laguna, California, including threatened populations of steelhead that use Laguna channels for seasonal passage to upstream breeding habitats. Current efforts to protect and enhance wetland habitats for migratory birds and waterfowl on the Pacific Flyway are substantially limited by Ludwigia growth, especially in the CDFG's Laguna Wildlife Area, site of the proposed Ludwigia control project (Sonoma County Water Agency, 2005). The Sonoma County Water Agency (2005) listed several dozen common and rare avian species that will benefit from Ludwigia removal in Laguna, California, because the growth of Ludwigia in this area actively promotes mosquito production, including mosquitos carrying the West Nile Virus, discovered in the area in 2004, which can kill native bird fauna.

Subrank II. Current Distribution and Abundance: High

6. Current Range Size in Nation:High significance
Comments: Ludwigia grandiflora was recently (Zardini et al., 1991; 1992) delineated as a distinct species from the Ludwigia uruguanyensis species complex, but confusion still exists, even in recent literature, as to whether Ludwigia grandiflora and Ludwigia hexapetala are distinct species or not. Taxonomically, many synonymies have not been reconciled and in North America, Ludwigia grandiflora and Ludwigia hexapetala have often been used interchangeably (Crow and Hellquist, 2000a; ITIS, 2005; Kartesz, 1999; Washington State Noxious Weed Control Board, 2006; Wittenberg, 2005), and are likely the same species. Global range of L. grandiflora includes two disjunct areas, one in southern Brazil, Bolivia, northeastern Argentina, Uruguay, and Paraguay (also locally in Guatemala), and the second (with relevance here) in the southeastern United States coastal plains of southern South Carolina, Georgia, northern Florida, and Louisiana, west to central Texas; and once in southwest Missouri (Zardini et al., 1991; Crow and Hellquist, 2000a). Ludwigia hexapetala was also similarly delineated but has since been synonymized with Ludwigia grandiflora. Its global range included southern Brazil, Uruguay, eastern Paraguay, and northern and central Argentina; also central Chile and scattered localities in Bolivia, Peru, Ecuador, Colombia, Costa Rica, and (introduced) widespread in the southeastern United States but scattered introductions elsewhere including California (Zardini et al., 1991) all the southeast and Gulf states (Benson et al., 2001) and north to New England (Benson et al., 2004). USDA (2006) lists the range in the U.S. as the eastern coastal states from New York to Florida (absent from Delaware and Maryland) through the Gulf states to Texas and up the Mississippi River drainage to Missouri; also California to Washington.

7. Proportion of Current Range Where the Species is Negatively Impacting Biodiversity:High/Moderate significance
Comments: In the southeastern and Gulf portions of the United States, water primrose has been considered a nuisance plant in most of its range (Benson et al., 2001; Chester and Holt, 1990; McGregor et al., 1996; Washington State Noxious Weed Control Board, 2006); as well as in some parts of California where it is locally common and Washington where it can dominate ditch margins in the Longview/Kelso Diking District in Cowlitz County (Washington State Noxious Weed Control Board, 2006; Zardini et al., 1991). In California, the worst Ludwigia infestations appear to be associated with symptoms of wetland degradation: thick sediments in shallow, slow-moving, nutrient-rich waters in full sun (Sonoma County Water Agency, 2005).

8. Proportion of Nation's Biogeographic Units Invaded:Moderate significance
Comments: It is conservatively estimated that between 35 and 40 ecoregions have been invaded by this species (Cordeiro, pers. obs. March 2006 based on TNC, 2001).

9. Diversity of Habitats or Ecological Systems Invaded in Nation:High significance
Comments: Found in coastal plains ponds where it forms a floating plant mat community favored by warm, southern climate (Hunt, 1943). It is a rooted herb found in areas of shallow water to about 1 meter deep with some flowing water tolerance that favors the margines of lakes, ponds, ditches, and streams (Washington State Noxious Weed Control Board, 2006). Also in shallow marshy areas, burrow pits, and ditches; as well as river banks and humid pastures (Wittenberg, 2005). In Oregon, southwestern Washington and California, Ludwigia is found at low elevations in rivers, streams, lakes, ponds, irrigation canals and other wet habitats (Sonoma County Water Agency, 2005).

Subrank III. Trend in Distribution and Abundance: High

10. Current Trend in Total Range within Nation:High/Moderate significance
Comments: This species is expanding rapidly in the United States beyond its original early invasion into the Pacific Northwest and the American southeast. It is now found in more than 20 states. Similar rapid expansion has been observed in some parts of Europe, particularly France (Dutartre, 2004; Wittenberg, 2005).

11. Proportion of Potential Range Currently Occupied:Medium/Low significance
Comments: Potential range unknown but it is estimated that this species could potentially occupy most, if not all, coastal states as well as all the states east of the Mississippi River excepting those in the western and central Great Lakes.

12. Long-distance Dispersal Potential within Nation:High significance
Comments: Aerial stems are killed by frost, but rhizomes will survive as indicated by the recent colonization of Ludwigia grandiflora in the continental climate of north-eastern France (Wittenberg, 2005). It also easily disperses by stem fragmentation with seed production uncommon. Growth is very rapid and biomass can double within 15 days in standing water (Wittenberg, 2005). In addition to to water currents, rooted fragments are also thought to be dispersed by birds or other wildlife (Sonoma County Water Agency, 2005).

13. Local Range Expansion or Change in Abundance:Moderate significance
Comments: This species has expanded rapidly in the past in the United States beyond its original early invasion into the Pacific Northwest and the American southeast. It is now found in more than 20 states with recent expansion continuing, though not as rapidly because a significant portion of its potential range has already been filled. Recent expansions in California have prompted the California Invasive Plant Council to rate Ludwigia as a High Impact invasive species due to its ability to rapidly invade unexploited ecosystems (Sonoma County Water Agency, 2005); and it is also listed as a noxious weed in Washington, Florida, North Carolina, and South Carolina. Recent rapid epansion is also documented in Tennessee and Kentucky (Chester and Holt, 1990).

14. Inherent Ability to Invade Conservation Areas and Other Native Species Habitats:High significance
Comments: Aerial stems are killed by frost, but rhizomes will survive as indicated by the recent colonization of Ludwigia grandiflora in the continental climate of north-eastern France (Wittenberg, 2005). It also easily disperses by stem fragmentation with seed production uncommon. Growth is very rapid and biomass can double within 15 days in standing water (Wittenberg, 2005). In France, this species has shown a high invasiveness adaptability as it was recently found growing in a large range of water and substrate quality, reproduces easily and quickly, fragments readily, and produces viable seeds and plantlets in the south part of France (highly unusual) (Dutartre, 2004). Along with the ability to tolerate low levels of oxygen, Ludwigia prospers in nutrient enriched water (Sonoma County Water Agency, 2005). In general, however, invasion depends on some form of disturbance, natural or anthropogenic.

15. Similar Habitats Invaded Elsewhere:Moderate significance
Comments: Ludwigia grandiflora is much more prevalent in streams (shallow, still, or flowing) in Europe than in the U.S., particularly in France where it has adapted to multiple flow conditions in rivers (Dutartre, 2004). Recently, this species has colonized wet grasslands in southern France (Wittenberg, 2005). Recent populations have been found in Sweden but it is not expected this species will pose any major problems there as the climate is largely too cold for this warmer climate species (Hallstan, 2005).

16. Reproductive Characteristics:High significance
Comments: Fragmentation of stems is the main mode of dispersal of Ludwigia spp. although reproduction by seeds is known though unusual (Sonoma County Water Agency, 2005). Individuals resprout readily when broken or cut and stems fragment very easily (see management). The role of seeds remains to be studied further (viable seeds were able to germinate in laboratory conditions but no data has yet been obtained in outdoor conditions).

Subrank IV. General Management Difficulty: High/Medium

17. General Management Difficulty:High/Moderate significance
Comments: Mechanical management can be used, however, it is essential to prevent the spread of plant fragments by creating filters downstream before carried out removal. All removed plants must be carefully disposed of to prevent fragment dissemination. Draining and sediment removal also is effective. Biological control is being investigated but is far from perfected. It mostly involves use of the water primrose flea beetle, Lysathia ludoviciana (McGregor et al., 1996) which naturally infects water primrose effectively reducing biomass. No method provides effective long-term control (Wittenberg, 2005). Herbicide control has been limited to a few herbicides only (McGregor et al., 1996). For example, the herbicide isoproturon was found to have only limited effectiveness on the related species, Ludwigia natans (= Ludwigia repens) (Feurtet-Mazel et al., 1996; Grollier et al., 1997). In Laguna, California, the Sonoma County Water Agency (2005) found that mechanical removal alone was essentially ineffective, and that the combined treatment of mechanical removal plus herbicidee treatment, though most expensive, gave the most lasting control. Ludwigia is a perennial weed, that re-sprouts readily from root and stem fragments. For this reason, biomass removals that do not completely eliminate the root system, or that are not done in conjunction with an herbicide treatment to kill the roots, can result in rapid re-growth. This is similarly true of flaming and crushing methods, and ignition is likely to be difficult in this aquatic environment.

18. Minimum Time Commitment:Moderate significance
Comments: No management method provides effective long-term control (Wittenberg, 2005). Dutarte (2004) quickly evaluated a few control methods in France and determined that hand-pulling and other mechanical removal are useful for small occurrences but are expensive, and herbicide application has only short-term efficiency. In Laguna, California, a control plan is being implemented. The initial phase of the Ludwigia Control Project plans an integrated pest management approach that includes 3 years of herbicide treatments to control Ludwigia plants in project areas, and mechanical removals to reduce further eutrophication from rotting vegetation, as well as 5 years of monitoring during and after treatments. Strategies for controlling Ludwigia over the long-term include restoring the riparian canopy to increase shading, developing a biological control program, and potentially dredging to increase water depth in key areas. Long-term goals also include reductions in nutrient loading and control of sediment inputs; other restoration-based control methods are actively being investigated (Sonoma County Water Agency, 2005).

19. Impacts of Management on Native Species:High/Moderate significance
Comments: Impacts on native species vary by control measure but it is assumed that most measures (herbicides, drainage, fire) impact non-target plant and animal species to varying degrees due to the broad nature of their application. For example, control by flooding followed by burning to remove will affect all species in an area. Draining and sediment removal has high negative impact on habitat and native species (Wittenberg, 2005). Biological control has just recently been investigated and some promise has been shown preliminarily for the flea beetle, Lysathia ludoviciana, which seems to have minimal impact on native species, but more studies are needed (McGregor et al., 1996). Usage recommendations for herbicides, including maximizing impact on Ludwigia and minimizing impact on natives (minimal effect was found for several glyphosate based herbicides), is discussed in detail in Sonoma County Water Agency (2005), although many herbicides are ineffective against this species.

20. Accessibility of Invaded Areas:Low significance/Insignificant
Comments: It appears most to all areas are easily accessible, as for most aquatic plants outside unusual habitats such as caves or high elevation streams or ponds. Because of the wide variety of aquatic and marshy habitats this species occupies, some areas may be difficult to access.

Other Considerations: Ludwigia grandiflora was recently (Zardini et al., 1991; 1992) delineated as a distinct species from the Ludwigia uruguanyensis species complex, but confusion still exists, even in recent literature, as to whether Ludwigia grandiflora and Ludwigia hexapetala are distinct species or not. Taxonomically, many synonymies have not been reconciled and in North America, Ludwigia grandiflora and Ludwigia hexapetala have often been used interchangeably (Crow and Hellquist, 2000a; ITIS, 2005; Kartesz, 1999; Washington State Noxious Weed Control Board, 2006; Wittenberg, 2005), and are likely the same species. Ludwigia grandiflora and Ludwigia hexapetala are treated as synonyms here.
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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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  • Benson, A.J., C.C. Jacono, P.L. Fuller, E.R. McKercher, and M.M. Richerson. 2004. Summary Report of Nonindigenous Aquatic Species in U.S. Fish and Wildlife Service Region 5. Report prepared for U.S. Fish and Wildlife Service, Arlington, Virginia, 29 February 2004. 142 pp.

  • Benson, A.J., P.L. Fuller, and C.C. Jacono. 2001. Summary Report of Nonindigenous Aquatic Species in U.S. Fish and Wildlife Service Region 4. Report prepared for U.S. Fish and Wildlife Service, Arlington, Virginia, 30 March 2001. 60 pp.

  • Chester, E.W. and S.E. Holt. 1990. The Uruguayian water-primrose (Ludwigia uruguayensis) in Tennessee and Kentucky. Journal of the Tennessee Academy of Science, 65(1): 9-12.

  • Crow, G.E. and C.B. Hellquist. 2000. Aquatic and Wetland Plants of Northeastern North America. A Revised and Enlarged Edition of Norman C. Fassett's A Manual of Aquatic Plants. Vol. 1, Pteridophytes, Gymnosperms, and Angiosperms: Dicotyledons. University of Wisconsin Press, Madison, Wisconsin. 448 pp.

  • Dutartre, A. 2004. Invasion and management of the water primrose (Ludwigia spp.) in France: a panorama. Oral presentation at 13th International Conference on Aquatic Invasive Species, September 2004, Ennis, County Clare, Ireland.

  • Feurtel-Mazel, A., T. Grollier, M. Grouselle, F. Ribeyre, and A. Boudou. 1996. Experimental study of bioaccumulation and effects of the herbicide isoproturon on freshwater rooted macrophytes (Elodea densa and Ludwigia natans). Chemosphere, 32(8): 1499-1512.

  • Grollier, T., A. Feurtet-Mazel, A. Boudou, and F. Ribeyre. 1997. Role of termperature on isoproturon bioaccumulation and effects on two freshwater rooted macrophytes: Elodea densa and Ludwigia natans. Ecotoxicology and Environmental Safety, 36: 205-212.

  • Hallstan, S. 2005. Global warming opens the door for invasive macrophytes in Swedish lakes and streams. M.S. Thesis, Swedish University of Agricultural Sciences, Uppsala, Sweden. 37 pp.

  • Hunt, K.W. 1943. Floating mats on a southeastern coastal plain reservoir. Bulletin of the Torrey Botanical Club, 70(5): 481-488.

  • Integrated Taxonomic Information System (ITIS). November 23-last update. Integrated Taxonomic Information System: Biological Names. Online. Available: http://www.itis.gov.

  • 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.

  • McGregor, M.A., D.R. Bayne, J.G. Steeger, E.C. Webber, and E. Reutebuch. 1996. The potential for biological control of water primrose (Ludwigia grandiflora) by the water primrose beetle (Lysathia ludoviciana) in the southeastern United States. Journal of Aquatic Plant Management, 34: 74-76.

  • Sonoma County Water Agency. 2005. Aquatic pesticide application plan for application of aquatic pesticides to portions of the Laguna de Santa Rosa consistent with Statewide General NPDES Permit for the Discharge of Aquatic Pesticides for Aquatic Weed Control in Waters of the United States Water Quality Order No. 2004-0009-DWQ. Plan Report submitted to Sonoma County, California, April 2005. 23 pp.

  • The Nature Conservancy. 2001. Map: TNC Ecoregions of the United States. Modification of Bailey Ecoregions. Online . Accessed May 2003.

  • Washington State Noxious Weed Control Board. 2006. Water Primrose (Ludwigia hexapetala (Hook. & Arn.) Zardini, Gu & Raven.). Written Findings of the State Noxious Weed Control Board - Class B Weed. Online. http://www.nwcb.wa.gov/weed%20info/Ludwigia_hexapetala.html. Accessed March 2006.

  • Wittenberg, R. (ed.). 2005. CABI Bioscience Switzerland report to the Swiss Agency for Environment, Forest and Landscape SAEFL. unpaginated.

  • Zardini, E.M., H. Gu, and P.H. Raven. 1991. On the separation of two species within the Ludwigia uruguayensis complex (Onagraceae). Systematic Botany, 16: 242-244.

  • Zardini, E.M., H. Gu, and P.H. Raven. 1992. Erratum: on the separation of two species within the Ludwigia uruguayensis complex (Onagraceae). Systematic Botany, 17(4): 692.

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