http://www.nps.gov/plants/alien/pubs/midatlantic/trna.htm http://www.nps.gov/plants/alien/pubs/midatlantic/trna.htm National Park Service - Water Chestnut "Trapa" http://www.nps.gov/plants/alien/pubs/midatlantic/trna.htm Water Chestnut http://www.nps.gov/plants/alien/pubs/midatlantic/trna.htm http://www.nps.gov/plants/alien/pubs/midatlantic/trna.htm Trapa natans http://www.nps.gov/plants/alien/pubs/midatlantic/trna.htm