Elodea looks very similar to Egeria and Hydrilla (see
below). There are however some distinctions for Elodea. In particular
this plant is smaller and has whorls of three (rarely 4). It is entirely
submersed except for its white flowers that are sent to the surface on
small, delicate shoots.
Elodea canadensis is a native species to the United states,
but can still be considered a weed because of its growth habits. It is
more of a noxious plant however, outside the US, in such areas as Asia
and Australia, where its not native.
canadensis is a plant that looks very similar to two other invasive
plants - Hydrilla verticillata and
Egeria densa. There are
however some easy ways to tell the difference. First of all, Egeria
has the largest leaves of any of them, growing up to 1/2 inch in diameter
and 3/4 to 5/4 inches long. Unlike Elodea, which is much smaller
and has whorls of 3 (rarely 4), Egeria has whorls of from 4-6, but never
3. Hydrilla usually has whorls of 5. Finally, while Elodea
and Egeria have smooth leaves, Hydrilla's feels rough
to the touch. This is because there are small teeth on the midrib. With
this information, you should be able to distinguish these three major
noxious aquatic plants.