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

Habitat: The species colonizes near shore habitats up to 3m deep and can adapt to a variety of habitats (Sousa et al. 2010).

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).

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).