Nuttall's Waterweed (Elodea Nuttallii) ERSS

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Nuttall’s Waterweed (Elodea nuttallii) Ecological Risk Screening Summary

U.S. Fish & Wildlife Service, May 2019 Revised, May 2019 Web Version, 10/24/2019

Photo: R. Vidéki. Licensed under Creative Commons BY-NC 3.0. Available: https://www.cabi.org/ISC/datasheet/20761. (May 3, 2019).

1 Native Range and Status in the United States Native Range From CABI (2019a):

“E. nuttallii is native to temperate North America common throughout most of the USA and south Canada […]”

Status in the United States From CABI (2019a):

“E. nuttallii is native to temperate North America common throughout most of the USA […]”

From Luizza et al. (2016):

“First documented in south central Alaska in 1982, little attention was paid to elodea [Elodea nuttallii and E. canadensis] until 2010 when the plants began to rapidly establish in lakes and slow-moving streams around Anchorage, Fairbanks, Cordova, and the Kenai Peninsula (Fairbanks CWMA 2014).”

According to USDA, NRCS (2019), Elodea nuttallii is listed as threatened in Kentucky and as a species of special concern in Tennessee.

From Carey (2016):

“Until recently, the aquarium trade transported Elodea into and around Alaska; however, the state barred importation of both E. canadensis and E. nuttallii, […]”

Figure 1. Map of the contiguous United States showing the native range of Elodea nuttallii (shaded in yellow). Map from U.S. Geological Survey (personal communication W. Daniel, USGS, Gainesville, Florida).

Means of Introductions in the United States From Schwoerer et al. (2019):

“Aquarium dumps are the likely vector near urban locations, while floatplanes are the most likely pathway responsible for long-distance dispersal into remote roadless [sic] locations (Hollander 2014). […] The discovery of Elodea 90 river miles downstream from an unmanaged infestation in Fairbanks was likely caused by flooding (Friedman 2015).”

Remarks From CABI (2019b):

“The introduction of the closely related and invasive E. nuttallii into Europe resulted in the displacement of E. canadensis [also invasive in Europe] from many localities where it had become well established (Simpson, 1990; Thiébaut et al., 1997; Barrat-Segretain, 2001; Larson, 2007).”

Although Elodea nuttallii is native to temperate North America, it is considered invasive in Alaska. As per the Service ERSS standard operating procedures, to determine the full extent of the plant’s risk to Alaska, an ERSS for the contiguous United States is completed before a more specific climate match can be completed for Alaska.

2 Biology and Ecology Taxonomic Hierarchy and Taxonomic Standing From ITIS (2019):

“Taxonomic Status: Current Standing: accepted”

“Kingdom Plantae Subkingdom Viridiplantae Infrakingdom Streptophyta Superdivision Embryophyta Division Tracheophyta Subdivision Spermatophytina Class Magnoliopsida Superorder Lilianae Order Alismatales Family Hydrocharitaceae Genus Elodea Species Elodea nuttallii (Planch.) H. St. John”

Size, Weight, and Age Range From CABI (2019a):

“Stem […] 30-100 cm long.”

Environment From CABI (2019a):

“[…] shoot elongation starts in spring when the temperature of the bottom reaches 10°C […]”

“E. nuttallii can be regarded as a low-light adapted plant, […] E. nuttallii is very tolerant of copper in particular and shows a high capacity to accumulate contaminants such as alkylphenols (Zhang et al., 2008).”

“E. nuttallii is able to grow in turbid, highly eutrophic waters (Cook and Urmi-König, 1985; Ozimek et al., 1993; Thiébaut and Muller, 1999), as well as in clear oligo-mesotrophic waters (Thiébaut et al., 1997; Barrat-Segretain, 2001; Nagasaka, 2004) with a certain degree of organic

pollution (Best et al., 1996). Growth of E. nuttallii is stimulated by fertilization with nitrogen and benefits from an excess of ammonia (Dendène et al., 1993).”

“It can occur to depths of 3 m (Simpson, 1990) and 5 m (Ikusima, 1984) where it develops into dense pure stands, but it is most frequently found in shallow water. Optimum pH has been found to be between 7 and 9 (Jones et al., 1993). It is tolerant of disturbance, oil pollution and is typically found in calcareous water, from fresh to slightly brackish coastal water (St John, 1965) up to 14 ppt salinity, and in fine sediment soil, where it is particularly successful.”

Climate/Range From CABI (2019a):

“All regions in which it is present are characterized by a temperate climate.”

Distribution Outside the United States Native The native range of Elodea nuttallii encompasses parts of the United States. See Section 1 for a full description of the native range.

From CABI (2019a):

“E. nuttallii is native to temperate North America common throughout most of […] south Canada […]”

Introduced From CABI (2019a):

“E. nuttallii was reported in Belgium in 1939 (with a definite identification in 1955) (Simpson, 1984); and in Britain in 1966, and spreading rapidly from 1970 onwards from the southeast and scattering throughout Wales, Scotland (Preston and Croft, 1997) and Ireland (1984). It was also reported in the Netherlands in 1941 and in Germany in 1961, where it has since spread across the country. There are also reports of finds in Denmark (1974) (DAISIE, 2009), in Switzerland, where it was reported in the 1980s, and is spreading along the Rodan (Rhone) river (CPS- SKEW, 2008). It was first found in Sweden in 1991, in Lake Mälaren (Anderberg, 1992) […]. Thereafter, its spread was noted in 1998 in the Danube delta in Romania, covering the majority of the delta (Sârbu et al., 2006); and from there to Slovakia in 2001 (Otahelová and Valachovic, 2002) and Hungary (Mesterházy et al., 2009) and then spreading into Western Europe (Wittenberg, 2005; Branquart, 2007). It is not unlikely that additional finds have been made, but that they have been mistaken for Canadian waterweed [Elodea canadensis]. In Asia, it was reported for the first time in 1960 in Japan (Lake Biwa) (Ikushima and [Kabaya], 1965). […] It was also introduced into China around the 1980s (Xu et al., 2007).”

In addition to the locations listed above, CABI (2019a) lists Elodea nuttallii as introduced and present in Austria, Czech Republic, France, Italy, Luxembourg, Poland, Slovenia, and the United

Kingdom, and as present in Finland and Norway. Pagad et al. (2018) list E. nuttallii as alien and verified in Belarus, Bulgaria, Croatia, Spain, Ukraine; and alien in Serbia.

Means of Introduction Outside the United States From CABI (2019a):

“E. nuttallii has been unintentionally introduced outside its natural range via the trade in live aquarium plants, and has spread by escaping from garden ponds and during the disposal of garden waste near waterways. As this species is sold commercially as an aquarium or garden plant, there is a high risk of unintentional introduction.”

From NIES (2019):

“Imported [to Japan] as an experimental material for physiology in 1920s-1930s.”

Short Description From CABI (2019a):

“E. nuttalli is a submerged-root aquatic plant, dioecious with floating flowers and rooting at nodes. The stems long and slender, often freely branched. Leaves pale green more or less equally spaced along the stem middle and upper leaves typically in whorls of 3 or occasionally 4, linear to narrowly lanceolate often recurved with folded margins; 6-13 mm long, 0.7-1.5 mm wide, acute at tip. Lower leaves in pairs and reduced in size, ovate-lanceolate. Stem slender, round in cross section, often freely branched, 30-100 cm long. Root white, unbranched, from nodes along the stem and not always present. The flower is small no more than 8 mm across; waxy white flowers occur at the ends of long, thread-like stalks and have 3 petals and usually 3 sepals. Male and female flowers occur on separate plants, but male flowers are rarely produced. Male flower spathes borne in middle axils, sessile, ovoid, about 2 mm long, spathe in 2 parts but the lobes twisted together so appears pointed; male flowers solitary and sessile in the spathe, breaking free and floating to the surface, where the flower opens, allowing pollen to drift on water's surface - hence the common name of free-flowering waterweed. Sepals ovate, about 2 mm long, sometimes reddish; petals lacking or to 0.5 mm long, ovate-lanceolate; stamens 9, pedicels briefly remaining attached following anthesis; inner 3 filaments connate proximally, forming column; anthers 1-1.4 mm; pollen in tetrads. Female flower spathes borne in upper axils, narrowly cylindric but slightly broadened at the base and the tip, 9-25 mm long; extended to the surface by a threadlike hypanthium up to 9 cm long; sepals green, tiny obovate, ca. 1 mm long; petals white, obovate, longer than the sepals; stigmas slender, slightly exceeding the sepals. Fruit narrowly ovoid to fusiform capsule, 5-7 mm long; containing several seeds. Ripens underwater. Seeds fusiform, 3.5-4.6 mm long, base with long hairs (Larson, 1993; FNA, 2009).”

From Kočić et al. (2014):

“In E. nuttallii, the extremes of the morphological variation are such that they appear to be distinct taxa in Europe, one with long, flat leaves, and the other with shorter, broader, strongly reflexed leaves (SIMPSON 1988, THIÉBAUT and DI NINO 2009).”

Biology From Maiz-Tome (2016):

“The species is found in shallow, still or slow-moving, slightly acidic to basic waters of lakes, ponds and rivers (New England Wild Flower Society 2011-2015).”

From CABI (2019a):

“E. nuttallii is dioecious; sexual reproduction occurs on the water surface, when the female flowers, […] are borne on long hypanthia and float on the water surface. The male flower, however, is released by abscission of the pedicel when still in bud. The bud contains a gas bubble and floats to the surface, where it opens to release the pollen (Bowmer et al., 1995; Preston and Croft, 1997). Fruiting specimens are very rare in North America (Lawrence 1976) and very few fully mature fruits were recorded in Canada (Catling and Wojtas, 1986). Although E. nuttallii reproduces both sexually and asexually by vegetative clonal propagation in its native range, in Europe the majority of plants are female, with the exception of a male colony known in Germany (Preston and Croft, 1997). In Japan all plants are male (Kunii 1984), so vegetative reproduction seems to be the dominant method of propagation - essentially by fragmentation and division of the stems and the production of winter buds from stem tips (Preston and Croft, 1997).”

“Phenological and seasonal patterns observed by Kunii (1984) in a pond in Japan, where abundance is high, show that shoot elongation starts in spring when the temperature of the bottom reaches 10°C; elongation ceases when the shoot reaches the surface water, and then a dense canopy is formed, with 40 to 65% of shoot biomass being found in the top 30 cm of water. […] Flowers appear in California from July to August (Hickman, 1993). The anchoring roots die at the end of September and then a large floating mat is formed that drifts up to the lake shore (Kadono, 2004). It sinks in December, when the water temperature drops below 10°C, and it can survive over winter, forming a dense mat of vegetation just above the lake bottom (Oki, 1994), with slight growth during winter if the temperatures are higher than 4°C (Kunii, 1981).”

“Populations of E. nuttallii may exhibit a high level of genetic polymorphism (Vanderpoorten et al., 2000). The number of basic chromosomes varies from 8 to 12, and the number of chromosomes of the populations varies according to country (2n = 32, 42, 44 in the USA, 2n = 48 in England, 2n = 48 in Britain, 2n = 44, 2n = 56 in France and Switzerland) (Thiebaut, 2008; FNA, 2009).”

From CABI (2019b):

“Erhard and Gross (2006) suggested that the production by both of allelochemicals that interfere with the growth of cyanobacteria and algae by E. canadensis and the closely related E. nuttallii could at least play some role in the success of these two species as invasives.”

Human Uses From CABI (2019a):

“E. nuttallii is used in cool water aquariums and it has a little economic importance in its native range.”

Diseases No records of diseases associated with Elodea nuttallii were found.

Threat to Humans From Josefsson (2011):

“No known effects to the human health.”

3 Impacts of Introductions From Kelly et al. (2015):

“The effects of E. nuttallii on species communities could be seen as both positive and negative, for example, the increased species richness of macrophyte species may be contrasted with the lower richness of algal taxa. Increases in floating plants associated with E. nuttallii can be contrasted with declines in submerged species. The association between floating plant species and E. nuttallii may arise as a result of structural complexity where E. nuttallii reaches the water surface, which reduces surface turbidity and provides anchorage for floating species.”

“In common with previous authors we found that plant density was significantly correlated with the biomass of invertebrate species living on macrophytes (Schultz and Dibble 2012). However, in our study plant density and invertebrate biomass did not differ between E. nuttallii and native plants, reflecting an explicit decision to examine differences between similar native and invasive plant beds. Whilst E. nuttallii may not alter the biomass of invertebrate species relative to similar-sized plants, results from our macrophyte dataset suggest that E. nuttallii may be replacing low-growing species and increasing overall macrophyte cover. Hence, by altering the relative regional abundance of different plant functional groups, E. nuttallii may produce corresponding changes in invertebrate biomass at larger spatial scales.”

“Higher oxygen saturation levels associated with E. nuttallii may have influenced species composition here: there was a lower abundance of some species groups associated with low oxygen saturation levels such as true fly larvae in the family Chironomidae, Alderflies (Sialis lutaria), leeches in the genera Erpobdella and Theromyzon, and Asellus isopods, and a higher abundance of some species associated with higher oxygen saturation such as caddisflies in the family Linephiidae. However, several species behaved contrary to expectation based on oxygen saturation alone, suggesting that other factors influence their distributions, for example damselflies in the family Coengriidae were negatively associated with E. nuttallii, leeches in the family Glossiphonidae were positively associated with E. nuttallii, and freshwater snails in the genera Hippeautis, Lymnea, Valvata, Physa and Bithynia, which have similar oxygen

requirements, show a range of different responses. Allelopathy may explain observed negative association between E. nuttalii and lepidopteran larvae in the family Pyralidae, as E. nuttalii has been previously shown to retard the growth and reduce the survival of the Pyralidae species Acentria ephemerella under laboratory conditions (Erhard et al. 2007).”

From Grudnik and Germ (2013):

“The considerable biomass produced by E. nuttallii modifies water flow, often increases the risk of flooding of adjacent land, competes with human activities (navigation, fishing, tourism) and is costly for management.”

“Based on our findings we can conclude that in the selected impoundments in the last five years E. nuttallii has successfully invaded stretches, which were not directly exposed to main water flow and prevailed over the native species M. spicatum.”

From Luizza et al. (2016):

“Even in Alaska’s Chena Slough, where elodea is present, it is believed to have displaced an entire population of arctic grayling (Thymallus arcticus; USFWS, personal correspondence 2014).”

From Mjelde et al. (2012):

“Diminished nutrient content in the sediment by E. nuttallii was also linked to the displacement of native species in Lake Kizaki (Nagasaka, 2004), […]”

From Josefsson (2011):

“In Ireland, hectares of water have become unfishable and unavailable for other aquatic recreational activities due to the growth of E. nuttallii (National Biodiversity Data Centre 2009).”

From CABI (2019a):

“E. nuttallii is included in the black list in Belgium (Branquart, 2007) and Switzerland (CPS- SKEW, 2008) because of its high environmental risk, so further introductions, at least in these regions, are unlikely.”

“E. nuttallii […] have the potential to develop into dense submerged beds, which prevent the use of water for recreational and professional purposes (Larson, 2003), navigation and port infrastructure (CPS-SKEW, 2008). The plant can also clog and impede drainage waterways.”

“E. nuttallii tends to dominate native macrophyte communities, which may lead to their local extinction. This species may also have a significant impact on protected sites.”

“It often forms dense, monospecific stands and displaces other aquatic plants from many localities (Simpson, 1984, 1990; Barrat-Segretain, 2005). E. nuttallii […] have shading effects during phases of rapid growth and mass occurrence. The plants compete with and displace indigenous vegetation, thus reducing biodiversity (Josefsson and Andersson, 2001).”

“Dense populations of plants reduce water movement, cut off light, produce anoxic conditions and trap sediments in the system. Plant decomposition at the end of the growing season typically induces a secondary eutrophication leading to the accumulation of end products toxic to many plants. In Japan, it has been reported that the biomass of native plants declined drastically after the invasion of E. nuttallii, which also has a competitive advantage over the native aquatic plants and competes with Ranunculus nipponicus and other species adapted to spring-fed water, threatening the unique ecosystems of Japan (Kadono, 2004). […] Impacts have also been recorded on invertebrate communities.”

From NIES (2019):

“Keeping of this species [Elodea nuttallii] in Saga Pref. [Japan] are controled [sic] by a prefectural ordinance. Import to Australia is prohibited.”

From Carey (2016):

“Until recently, the aquarium trade transported Elodea into and around Alaska; however, the state barred importation of both E. canadensis and E. nuttallii, […]”

4 Global Distribution

Figure 2. Known global distribution of Elodea nuttallii. Map from GBIF Secretariat (2019). The locations in Africa and Australia were not used to select source points for the climate match. According to the record information for the location in Africa, that specimen was collected in California and not Burkina Faso (GBIF Secretariat 2019). The locations in Australia are based off DNA sequences collected from a marine environment and not the observation or collection of an actual specimen (GBIF Secretariat 2019).

Additional locations in eastern Slovenia are given in Grudnik and Germ (2013) and in northeastern Croatia by Kočić et al. (2014).

Elodea nuttallii is listed as present in Hungary, Poland, Romania, Slovakia, Slovenia, Bulgaria, Spain, Ukraine, and Serbia (Pagad et al. 2018; CABI 2019a) but no georeferenced observations were available from those countries to use in selecting source points for the climate match. It is the opinion of the author that the absence of these points does not significantly affect the results of the climate match and does not warrant a lower certainty in the results of the match.

5 Distribution Within the United States

Figure 3. Known distribution of Elodea nuttallii in the contiguous United States. Map from BISON (2019).

Figure 4. Known distribution of Elodea nuttallii in the Alaska. Map from U.S. Geological Survey (2019).

6 Climate Matching Summary of Climate Matching Analysis Elodea nuttallii is native to most of the contiguous United States and the corresponding climate match was mostly high. There were areas of medium match in the south from Georgia in the east to Arizona and New Mexico in the west, and along the Pacific Coast. There were small areas of low match in southern peninsular Florida, and southern Texas. Everywhere else had a high match. The Climate 6 score (Sanders et al. 2018; 16 climate variables; Euclidean distance) for contiguous United States was 0.925, high. The range for a high climate score is 0.103 and above. All States had high individual Climate 6 scores.

Figure 5. RAMP (Sanders et al. 2018) source map showing weather stations in North America, Europe, and Japan selected as source locations (red) and non-source locations (gray) for Elodea nuttallii climate matching. Source locations from Grudnik and Germ (2013), Kočić et al. (2014), BISON (2019), GBIF Secretariat (2019), and U.S. Geological Survey (2019). Selected source locations are within 100 km of one or more species occurrences, and do not necessarily represent the locations of occurrences themselves.

Figure 6. Map of RAMP (Sanders et al. 2018) climate matches for Elodea nuttallii in the contiguous United States based on source locations reported by Grudnik and Germ (2013), Kočić et al. (2014), BISON (2019), GBIF Secretariat (2019), and U.S. Geological Survey (2019). Counts of climate match scores are tabulated on the left. 0 = Lowest match, 10 = Highest match.

The High, Medium, and Low Climate match Categories are based on the following table:

Climate 6: Proportion of Climate Match (Sum of Climate Scores 6-10) / (Sum of total Climate Scores) Category 0.000≤X≤0.005 Low 0.005

7 Certainty of Assessment The certainty of assessment for Elodea nuttallii is high. There is quality information available about the biology, ecology, and distribution of the plant. Peer-reviewed and grey literature documents introductions and impacts from introductions.

8 Risk Assessment Summary of Risk to the Contiguous United States Nuttall’s waterweed (Elodea nuttallii) is a freshwater aquatic plant native to North America, including much of the contiguous United States. The plant grows fully submerged except for the flowers and may create large, dense beds. There is some trade in this plant in the aquarium industry. The history of invasiveness for E. nuttallii is high. It has been introduced around the world and in Alaska. Established populations have had impacts such as changes in species richness, altering invertebrate species composition, out-competing native plants, changes to sediment nutrients, and dense beds can impact flooding and recreational uses of waterways. It may have displaced a population of native fish in Alaska. There are regulations to control the trade of this species in Belgium, Switzerland, Japan, and Australia. The climate match is high for most of the United States, where the plant is native. There were few areas, mainly in the Deep South that did not have a high climate match. The certainty of assessment is high. Quality information is available and the history of invasiveness is documented in peer-reviewed and grey literature. The overall risk assessment category is high.

Assessment Elements  History of Invasiveness (Sec. 3): High  Climate Match (Sec. 6): High  Certainty of Assessment (Sec. 7): High  Remarks/Important additional information: No additional remarks.  Overall Risk Assessment Category: High

9 References Note: The following references were accessed for this ERSS. References cited within quoted text but not accessed are included below in Section 10.

BISON. 2019. Biodiversity Information Serving Our Nation (BISON). U.S. Geological Survey. Available: https://bison.usgs.gov. (May 2019).

CABI. 2019a. Elodea nuttallii (Nuttall’s waterweed) [original text by M. A. Duenas]. In Invasive Species Compendium. CAB International, Wallingford, U.K. Available: https://www.cabi.org/ISC/datasheet/20761. (May 2019).

CABI. 2019b. Elodea canadensis (Canadian pondweed) [original text by I. Popay and H. Dawson]. In Invasive Species Compendium. CAB International, Wallingford, U.K. Available: https://www.cabi.org/ISC/datasheet/20759. (May 2019).

Carey, M. P., S. A. Sethi, S. J. Larsen, and C. F. Rich. 2016. A primer on potential impacts, management priorities, and future decisions for Elodea spp. in high latitude systems: learning from the Alaskan experience. Hydrobiologia 777:1–19.

GBIF Secretariat. 2019. GBIF backbone taxonomy: Elodea nuttallii St. John. Global Biodiversity Information Facility, Copenhagen. Available: https://www.gbif.org/species/5329212. (May 2019).

Grudnik, Z. M., and M. Germ. 2013. Spatial pattern of native species Myriophyllum spicatum and invasive alien species Elodea nuttallii after introduction of the latter one into the Drava River (Slovenia). Biologia 68(2):202–209.

ITIS (Integrated Taxonomic Information System). 2019. Elodea nuttallii (Planch.) H. St. John. Integrated Taxonomic Information System, Reston, Virginia. Available: https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=502 246. (May 2019).

Josefsson, M. 2011. NOBANIS – invasive alien species fact sheet – Elodea canadensis, Elodea nuttallii and Elodea callitrichoides. Online database of the European Network on Invasive Alien Species – NOBANIS. Available: https://www.nobanis.org/globalassets/speciesinfo/e/elodea-canadensis/elodea.pdf. (May 2019).

Kelly, R., C. Harrod, C. A. Maggs, and N. Reid. 2015. Effects of Elodea nuttallii on temperate freshwater plants, microalgae and invertebrates: small differences between invaded and uninvaded areas. Biological Invasions 17(7):2123–2138.

Kočić, A., J. Horvatić, and S. D. Jelaska. 2014. Distribution and morphological variations of invasive macrophytes Elodea nuttallii (Planch.) H. St. John and Elodea canadensis Michx in Croatia. Acta Botanica Croatica 73(2):437–446.

Luzzia, M. W., P. H. Evangelista, C. S. Jarnevich, A. West, and H. Stewart. 2016. Integrating subsistence practice and species distribution modeling: assessing invasive elodea’s potential impact on Native Alaskan subsistence of Chinook Salmon and whitefish. Environmental Management 58:144–163.

Maiz-Tome, L. 2016. Elodea nuttallii. The IUCN Red List of Threatened Species 2016: e.T64311330A67729386. Available: https://www.iucnredlist.org/species/64311330/67729386. (May 2019).

Mjelde, M., P. Lombardo, D. Berge, and S. W. Johansen. 2012. Mass invasion of non-native Elodea canadensis Michx. in a large, clear-water, species-rich Norwegian lake – impact on macrophyte biodiversity. Annales de Limnologie - International Journal of Limnology 48:225–240.

NIES (National Institute for Environmental Studies). 2019. Elodea nuttallii. In Invasive species of Japan. National Research and Development Agency, National Institute for Environmental Studies, Tsukuba, Japan. Available: https://www.nies.go.jp/biodiversity/invasive/DB/detail/80680e.html. (May 2019).

Pagad, S., P. Genovesi, L. Carnevali, D. Schigel, and M. A. McGeoch. 2018. Introducing the Global Register of Introduced and Invasive Species. Scientific Data 5:170202.

Sanders, S., C. Castiglione, and M. Hoff. 2018. Risk assessment mapping program: RAMP, version 3.1. U.S. Fish and Wildlife Service.

Schwoerer, T., J. M. Little, and M. D. Adkison. 2019. Aquatic invasive species change ecosystem services from the world’s largest wild sockeye salmon fisheries in Alaska. Journal of Ocean and Coastal Economics 6(1):2.

U.S. Geological Survey. 2019. Elodea nuttallii species point map. U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, Florida. Available: https://nas.er.usgs.gov/viewer/omap.aspx?SpeciesID=2975. (May 2019).

USDA, NRCS. 2019. Elodea nuttallii. The PLANTS database. National Plant Data Team, Greensboro, North Carolina. Available: https://plants.usda.gov/core/profile?symbol=ELNU2. (May 2019).

10 References Quoted But Not Accessed Note: The following references are cited within quoted text within this ERSS, but were not accessed for its preparation. They are included here to provide the reader with more information.

Anderberg, A. 1992. Nuttall waterweed, Elodea nuttallii, a new macrophyte in the Swedish flora. Svensk Botanisk Tidskrift 86:43–45.

Barrat-Segretain, M. H. 2001. Invasive species in the Rhône River floodplain (France): replacement of Elodea canadensis Michaux by E. nuttallii St. John in two former river channels. Archiv für Hydrobiologie 152(2):237–251.

Barrat-Segretain, M. H. 2005. Competition between invasive and indigenous species: impact of spatial pattern and developmental stage. Plant Ecology 180(2):153–160.

Best, E. P. H., H. Woltman, and F. H. H. Jacobs. 1996. Sediment-related growth limitation of Elodea nuttallii as indicated by a fertilization experiment. Freshwater Biology 36(1):33– 44.

Bowmer, K. H., S. W. L. Jacobs, and G. R. Sainty. 1995. Identification, biology and management of Elodea canadensis, Hydrocharitaceae. Journal of Aquatic Plant Management 33:13–19.

Branquart, E. 2007. Alert, black and watch lists of invasive species in Belgium. Elodea nuttalli - Nuttall's waterweed Harmonia version 1.2, Belgian Forum on Invasive species. Available: http://ias.biodiversity.be.

Catling, P. M., and W. Wojtas. 1986. The waterweeds (Elodea and Egeria, Hydrocharitaceae) in Canada. Canadian Journal of Botany 64:1525–1541.

Cook, C. D. K., and K. Urmi-König. 1985. A revision of the genus Elodea (Hydrocharitaceae). Aquatic Botany 21(2):111–156.

CPS-SKEW. 2008. Black List and Watch List. Swiss Commission for Wild Plant Conservation CPS/SKEW. Available: http://www.cps-skew.ch/english/black_list.htm.

DAISIE. 2009. Elodea nuttallii. Delivering Alien Invasive Species Inventories for Europe. European Invasive Alien Species Gateway. Available: http://www.europe-aliens.org/.

Dendène, M. A., T. Rolland, M. Trémolières, and R. Carbiener. 1993. Effect of ammonium ions on the net photosynthesis of three species of Elodea. Aquatic Botany 46(3-4):301–315.

Erhard, D., and E. M. Gross. 2006. Allelopathic activity of Elodea canadensis and Elodea nuttallii against epiphytes and phytoplankton. Aquatic Botany 85(3):203–211.

Erhard, D., G. Pohnert, and E. M. Gross. 2007. Chemical defense in Elodea nuttallii reduces feeding and growth of aquatic herbivorous Lepidoptera. Journal of Chemical Ecology 33:1646–1661.

Fairbanks CWMA (Fairbanks Cooperative Weed Management Area). 2014. Available: http://www.fairbanksweeds.org. [Source material did not give full citation for this reference.]

FNA. 2009. Elodea nuttallii. Flora of North America, volume 22. Missouri Botanical Garden, St. Louis. Available: http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=222000059.

Friedman, S. 2015. Invasive Elodea found north of Nenana; first interior sighting beyond Fairbanks area. Fairbanks Daily News Miner, September 1, 2015. Available: http://www.newsminer.com/news/local_news/invasive-elodea-found-north-of-nenana- firstinterior-sighting-beyond/article_cd427cf0-511d-11e5-8c60-c733aa6798ec.html.

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