Non-native to Chesapeake Bay; invasive - Family -
Hydrocharitaceae - Distribution - Hydrilla is an exotic species
introduced from southeast Asia which first appeared in United
States during 1960's. Today it is found in most of the
southeastern United States, westward to California. Hydrilla was
first observed in 1982 in the Potomac River near Washington D.C.
and by 1992 grew to cover 3000 acres in the Potomac. Hydrilla is
also found in the Susquehanna Flats and a few upper bay
tributaries. It is predominantly a freshwater species, but has
been found in waters of 6-9 ppt salinity. Hydrilla grows on
silty to muddy substrates and tolerates lower light than other
bay - Recognition - Stems are freely branching with whorls of
3-5 leaves linear to lanceolate leaves. Leaves have strongly
toothed or serrated margins and a spinous midrib. Roots are
adventitious, forming along nodes of rhizomes that grow
horizontally atop or just below sediment surface. Tubers are
also commonly found at the end of runners that branch fr