Common Hornwort (Ceratophyllum demersum)
USGS - Northern Prairie Wildlife Research Center
<a rel="nofollow" class="external free" href="https://www.npwrc.usgs.gov/resource/1999/neflor/species/6/cerademe.htm">http://www.npwrc.usgs.gov/resource/1999/neflor/species/6/cerademe.htm</a>