MONITORING INVASIVE SUBMERSED AND FLOATING-LEAF PLANTS IN THE UPPER MISSISSIPPI 
RIVER SYSTEM - WHAT SHOULD WE WATCH FOR?

Heidi A. Langrehr.  Wisconsin Department of Natural Resources, Onalaska Field 
Station, Onalaska, WI 54650

Invasive species are a serious problem throughout the world.  An invasive is any 
species that is introduced into a habitat where it is not native.  Because there 
are few predators, parasites, or pathogens to keep invasive species in check, 
they often explode in number and crowd out native species.  Two invasive 
submersed plant species, Eurasian watermilfoil (Myriophyllum spicatum L.) and 
curly pondweed (Potamogeton crispus L.) occur commonly in the Upper Mississippi 
River System (UMRS) and have caused problems inland in Minnesota and Wisconsin.  
From 1998 through 2001, 550 to 670 sites were sampled for submersed and 
floating-leaf plants in each of three pools (4, 8, and 13) of the UMRS through 
the Long Term Resource Monitoring Program.  Although both Eurasian watermilfoil 
and curly pondweed have been recorded in all three pools, so far neither species 
has dominated the submersed plant community.  Other invasive species have the 
potential to spread to the UMRS.   Submersed species include hydrilla (Hydrilla 
verticillata [L.] Royle) and fanwort (Cabomba caroliniana Gray).  Floating-leaf 
species include European frogbit (Hydrocharis morsus-ranae L.) and water 
chestnut (Trapa natans L.).  Hydrilla is listed on the Federal noxious weed list 
and has caused infestation problems in Washington State.  Hydrilla has been 
recorded as far north as Massachusetts in eastern United States.  Fanwort is 
listed on Washington State's noxious weed list and has been found in Michigan, 
Illinois, and at nuisance levels in Canada.  European frogbit is listed as one 
of Canada's principal invasive aliens and has been found along Michigan's 
eastern coast as well as in New York State.  The Wisconsin Department of Natural 
Resources has listed water chestnut as a potential problem species and it is on 
New York State's top twenty invasive plants list.  Aquatic and Wetland Plants of 
Northeastern North America (G.E. Crow and C.B. Hellquist 2000) list several 
other species with the potential to become a nuisance in northeastern United 
States.  Submersed species include two milfoils (Myriophyllum heterophyllum 
Michx. and M. aquaticum [Vell.] Verdc.), Brazillian waterweed (Egeria densa 
Planch.), and minor naiad (Najas minor All.).  Floating-leaf species include 
water fern (Marsilea quadrifolia L.) and yellow floating heart (Nymphoides 
peltata [Gmel.] Kuntze).  These species have a more southern range and are not 
as likely to grow to nuisance levels in the UMRS or have not been reported at 
nuisance levels in northern United States or Canada.

Keywords:  invasive plants, submersed plants, floating-leaf plants, monitoring