Anacharis najas (Planchon) Victorin 1931, Elodea najas, narrowleaf egeria

Tolerances: Often the dominant species, E. najas successfully photosynthesizes in low light and turbid environments, allowing it to outcompete species (Tavechio 2003, Bini et al. 2010). It can also substitute bicarbonate for growth when dissolved carbon dioxide levels are low (Pierini and Thomaz 2004). The species prefers waters with conductivity levels of 60-110 microsiemens and can tolerate pH levels of 6.5-10.0 though rates of photosynthesis peak between a pH of 8.0-8.8 (Pierini and Thomaz 2004, Bini and Thomaz 2005). The lack of complex root structure prevents the plant from colonizing habitats with strong water flow and the rapid decomposition of fragments during warmer months limits its colonization ability (Carvahlo et al. 2005).

Reproduction: Seed production and therefore sexual reproduction of E. najas has rarely been observed in the wild. Egeria najas is not thought to be a sterile species however pollen transfer has rarely been observed. In natural populations of E. najas, W. Briicker and B. Luond (personal communication, 1981 in Cook and Urmi-König 1984) found that usually both sexes were present and that male flowers out-numbered females by about 4:1 or 3:1. Developing fruits with fertilized seeds were collected on 27 November 1981 (near Corrientes, Argentina), the fruits probably ripen somewhat later (Cook and Urmi-König 1984).Most reproduction of E. najas is asexual via fragmentation. Viable fragments break off at points of “double nodes”, where they are able to grow without being fully anchored in sediment (Cook and Urmi-König 1984). Roots and shoots will grow concurrently. Root fragments are able to withstand short periods of desiccation, especially in habitats that are oligotrophic or possess sand substrate (Silveira et al. 2009).

Potential pathway(s) of introduction: Unauthorized intentional release, Stocking/Planting/Escape from recreational culture.

The most likely pathway of introduction for E. najas is via unauthorized intentional release through stocking and planting or escape from recreational culture. E. najas is widely available through the online aquarium trade at websites such as Amazon, eBay, and Etsy. There, shoppers can purchase live plants for installation into aquariums and ponds; however there is not enough information to determine the frequency of E. najas plantings. Nor is there enough information to determine if E. najas is commercially cultured in the Great Lakes.

The species is not known to be taken up in ballast water. However, once established in the basin, introduction via hitchhiking becomes far more likely as the species is able to survive for several days outside of water, even when desiccated (Silveira et al 2009).

Egeria najas has a moderate probability of establishment if introduced to the Great Lakes (Confidence level: High).

Egeria najas is a highly adaptable species that can survive in a variety of conditions. Most notably, the species is tolerant to low light conditions that allowed it to become the dominant species in its native range (Bini and Thomaz 2005). However, the species’ simple root structure prevents its establishment in ecosystems with strong currents (Sousa et al. 2010). Additionally, while the congeneric species, E. densa, established itself in several Great Lake states, it is unknown whether or not E. najas would be able to successfully overwinter in the Great Lakes basin (USGS) under the current climate.

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

Environmental	Socioeconomic

The species forms dense mats concentrated just below the water surface, blocking sunlight from penetrating the water column to the detriment of photosynthetic organisms(Thomaz et al. 1999, Bini et al. 2010, Sousa et al. 2010). The loss of light may also impair the ability of predators to capture prey, as many aquatic predators rely on sight to capture prey. The species has been found to lower dissolved oxygen concentrations within patches down to 6.5 mgL-1, negatively impacting fish and other aquatic species (Bini et al. 2010).

Egeria najas has the potential for high socioeconomic impact if introduced to the Great Lakes.

In forming dense mats, E. najas populations can clog hydroelectric facilities, interrupting energy production and requiring millions of dollars to manage the species annually (Mori 2012).

Egeria najas has the potential for moderate beneficial impact if introduced to the Great Lakes.

Patches of E. najas increase the habitat complexity of lentic habitats. This increased complexity creates additional microhabitats for organisms to utilize. Fish larvae use the mats for shelter in order to avoid predation from predatory insects and other piscivores (Pelicice 2006, Carniatto 2020). E. najas also provides similar ecosystem services for periphytic algae (Neif et al. 2014).

The species is not on the Illinois Aquatic Life Approved Species List and is illegal to be imported or possessed alive without a permit (515 ILCS 5/20-90).

Note: Check federal, state/provincial, and local regulations for the most up-to-date information.

Control
Biological

While not native to E. najas’ native range, grass carp (Ctenopharyngodon idella) demonstrated the ability and mild preference for consuming E. najas in a laboratory setting (Silva 2014). Grass carp are a non-native species found in several of the Great Lakes. This species was first imported to the United States in 1963 to aquaculture facilities in Auburn, Alabama, and Stuttgart, Arkansas (Guillory and Gasaway 1978). 

Physical

Mechanical methods center around water drawdowns of reservoirs when the species is present (Bini and Thomaz 2005, Thomaz et al. 2006, Florencio et al. 2021). In Thomaz et al. (2006), water drawdowns led to significant decreases in E. najas biomass. However, these decreases in biomass were temporary. Water drawdowns lead to the species migrating to “new” nearshore habitat and if water levels increase, the species will recolonize previous habitat.

Chemical

Chemical control methods focus on the use of herbicide ingredients diquat and fluridone. The two chemicals have been shown to significantly reduce the living biomass of E. najas. Diquat is the more effective of the two herbicides and more effectively controls the species at concentrations of 0.5 and 1.0 mgL-1 (Martins et al. 2007).  Research has also shown that multiple applications of herbicide are necessary to control the species and that effectiveness of herbicide application ranges with some studies reporting instances of eradication while others report that E. najas biomass rebounded once herbicide application ended (Marcondes et al. 2003, Martins et al. 2008).

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.