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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: narrowleaf anacharis

Synonyms and Other Names: Anacharis najas (Planchon) Victorin 1931, Elodea najas, narrowleaf egeria

Identification: According to Cook and Urmi-König (1984):

Habit: dioecious, submerged, freshwater perennial forb

Stems/Roots: adventitious (developing at nodes) roots; irregular branching at double nodes (two nodes close together)

Leaves: scale-like or elongate, recurved, visibly serrated, usually in whorls of 5 leaves

Flowers: unisexual plants (dioecious), flowers originating from an apical spathe, three white petals much larger than the sepals

Fruits/Seeds: fusiform, sessile fruits, uncommon due to dioecious plants not typically being found together

Look-a-likes: Other anacharoids in the Hydrocharitaceae family (Hydrilla verticillata, Egeria densa, Elodea canadensis, Elodea nuttallii); Egeria najas has distinctive curved, serrated leaves and large flower petals

Size: up to 3 m in length or longer (Cook and Urmi-König 1984)

Native Range: South America (Argentina, Brazil, Paraguay, and Uruguay) (Cook and Urmi-König 1984)

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

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

Ecology:

Habitat: found at about 1 m depth in slow-moving or still water (lentic) in native Argentina (Cook and Urmi-König 1984)

Life history: Egeria najas lacks dormant structures (hibernacula), and seed is not found in wild populations (Cook and Urmi-König 1984). Dispersal is via fragmentation of double nodes (shorter than usual internodes), which can produce new stems and roots.

Tolerances: Light penetration strongly influences E. najas root and shoot growth (Tavechio and Thomaz 2003). Under light attenuation, increased temperatures caused increased decomposition rates for E. najas (Carvalho et al. 2005).

Community: common associated genera in native Argentina include Mayaca, Utricularia, Cabomba, Salvinia, Pistia, Limnobium, Hydrocleys, Nymphoides, Alternanthera, Eichhornia, Pontederia, Reussia, and Echinodorus (Cook and Urmi-König 1984)

Means of Introduction: Egeria najas is available in the plant nursery trade, and likely is released via aquarium dumping.

Status: The residential pond population in Hillsborough County, FL was eradicated in 2018 after chemical treaments (G. Lokuta, pers. comm. 2019).

Impact of Introduction: 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).

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).

References: (click for full references)

Bini L.M., S. M. Thomaz and P. Carvalho. 2010. Limnological effects of Egeria najas Planchon (Hydrocharitaceae) in the arms of Itaipu Reservoir (Brazil, Paraguay). Limnology 11(1):39-47. https://doi.org/10.1007/s10201-009-0286-4.

Carvalho, P., S.M. Thomaz, and L.M. Bini. 2005. Effects of temperature on decomposition of a potential nuisance species: the submerged aquatic macrophyte Egeria najas Planchom (Hydrocharitaceae). Brazilian Journal of Biology 65(1):51-60. http://dx.doi.org/10.1590/S1519-69842005000100008.

Cook, C.D.K., and K. Urmi-König. 1984. A revision of the genus Egeria (Hydrocharitaceae). Aquatic Botany 19(1-2):73-96.

Lokuta, G. 2019. Personal Communication. Florida Fish and Wildlife Conservation Commission.

Mori E. S., D. Martins, E.D. Velini, C.L. Marino, C.F. Gouvea, S.M.M. Leite, E. Camacho Palomino, and R.P. Curies. 2012. Genetic diversity in Egeria densa and E. najas in Jupia Reservoir, Brazil. Ciencia e Investigacio´n Agraria 39(2):321-330. http://dx.doi.org/10.4067/S0718-16202012000200008.

Sousa W., S.M. Thomaz, and K.J. Murphy. 2010. Response of native Egeria najas Planch. and invasive Hydrilla verticillata (L.f.) Royle to altered hydroecological regime in a subtropical river. Aquatic Botany 92(1):40-48. https://dx.doi-org/10.1016/j.aquabot.2009.10.002.

Tavechio, W.L.G., and S.M. Thomaz. 2003. Effects of light on the growth and photosynthesis of Egeria najas Planchon. Brazilian Archives of Biology and Technology 46(2):203-209. http://dx.doi.org/10.1590/S1516-89132003000200011.

Thomaz S.M., L. M. Bini, M. C. de Souza, K. K. Kita and A. F. M. Camargo. 1999. Aquatic macrophytes of Itaipu reservoir, Brazil: Survey of species and ecological considerations. Brazilian Archives of Biology and Technology 42(1):15-22. https://dx.doi-org/10.1590/S1516-89131999000100003.

Author: Pfingsten, I.A., D. Rose

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.