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Hydrilla - Hydrilla verticillata
Family: Hydrocharitaceae

Description

Hydrilla is a noxious weed native, we think to Asia, although it has spread widely across the globe today. This plant has leaves in whorls of normally 5. It has serrations or small spines on the midrib, of which is also slightly reddish when fresh.

Interesting facts

Hydrilla is considered the most problematic aquatic plant in the United states. Part of the reason for this is because of its fast growth and its ability to regenerate from tubers and from fragments.

Hydrilla is a plant that looks very similar to three other invasive plants - Egeria densa and Elodea canadensis. 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.

Crew Experiences

Rob Nelson: "For three years I worked at an aquatic plant research facility in North Texas (LAERF). I worked as a researcher, trying to help understand both how native systems are effected by invasive plants and how to control the spread of these invaders. Probably the worst aquatic plant we had to deal with was Hydrilla. Hydrilla can withstand a drawdown (no water in a pond) for several years, it can withstand intense heat, and its impossible to get rid of by mechanical extraction alone. We tried chemical means, which unfortunately kill the natives as well. We finally tried to examine biocontrol as a viable option to reduce plant stock."

"For several years, different controlled, and isolated experiments on Hydrilla were conducted with an introduced fly from Pakistan. This fly had larvae the drilled into the hydrilla stems and essentially caused the entire plant to be so severely disabled that it could no longer compete with natives species."

"Today the research that has been done through the Army Corp of Engineers in Lewisville and in Vicksburg Mississippi has concluded that there is no danger to native populations, and because of that the fly has been introduced to several lakes and rivers. One of the best examples of this is the infestation of the Rio Grande River, which has now been successfully controlled."

VIDEO

Links to more information

Plant information - Aquatic plants of Washington
Description and Management - Western Aquatic Plant Management Society
Links to lots of information about Hydrilla - InvasiveSpecies.org