HYDRILLA 



Hydrilla verticillata Royle 



Hydrilla is an extremely prolific aquatic plant that has infested 

 millions of acres of lakes, rivers, and irrigation systems throughout the 

 United States. The plant is not a native species. Thought to have been 

 imported originally for aquarium use, it was first discovered in a Florida 

 river and drainage canal in 1960. 



Hydn'llahdiS two to eight leaves per whorl along its long branching 

 stems. The leaves are spear shaped, the length is approximately five 

 to seven times the width, and the leaf margins are serrated. Hydrilla 

 is often confused with waterweed {Elodea canadensis ^\c\\\.) which 

 has very similar vegetative growth habits. However, several 

 characteristics distinguish the two species ( 1 ) Hydrilla has one to three 

 tiny spines along the central vein on the underside of the leaves, which 

 waterweed lacks; (2) Hydrilla leaf margins are serrated, but waterweed 

 leaf margins are either smooth or finely serrated (insert 1); (3) Turions 

 form in the axils of hydnlMeaves (insert 2); and (4) Potato-like tubers 

 appear in the soil on the ends of the rhizomes (insert 3). Waterweed 

 produces neither turions or tubers. 



Hydrilla zho produces small, white female flowers (insert 4) which 

 appear as six simple pedals at the end of a long threadlike stalk. They 

 may be observed on or near the water surface in late summer or early 

 fall. Male flowers, and consequently fruits, have not been observed in 

 the United States. 



Hydrilla reproduces by vegetative fragments, stolons, turions, and 

 tubers. Control efforts are very difficult because turions and tubers are 

 able to survive winter and stress periods. 



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