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Name derivation:

Egeria is a legendary water nymph.


Egeria Planch.

Order Hydrocharatales;  Family Hydrocharataceae


Stems elongate, more than 3 cm and up to >2 m long, erect; leaves cauline, whorled.  Whorls with 5 or more leaves per node.

Only the flowers are on the water surface.  Dioecious (separate male and female plants), hydrophyllous pollination (on the water surface).

All E. densa plants in the USA are male, so reproduction is entirely vegetative (by stem fragmentation), producing a widespread clone.

Similar genera:

Elodea has whorls with 2-4 (up to 7) leaves per node or leaves opposite at most proximal nodes  Hydrilla has “prickles” along abaxial surface of midvein


Freshwater lakes.  Native to S. America (Argentina, Brazil, and Uruguay).  Elsewhere considered a nuisance invasive genus, especially E. densa (‘Brazilian Elodea’).  Widely distributed globally, often introduced as an aquarium plant.

Thick mats of foliage obstruct water flow in aquaducts, migration of anadromous fish, and human recreation (swimming, boating, water skiing).  They also outcompete native aquatic vegetation for space.