Azolla cristata Kaulf.
Family: Salviniaceae
[Azolla mexicana C.Presl]
Azolla cristata image
James Reveal  
Azolla cristata image
University of Wisconsin-Stevens Point, Robert W. Freckmann Herbarium (UWSP)  
Etymology: Azolla: name obscure
Plants: annual/perennial, aquatic fern either green or blue-green to dark red or with just the edges bright red; free-floating or in 1 1/2" thick multi-layered mats
Conservation Status: Native