Each tiny Wolffia plant is a rootless oval body, producing a pistil (stigma) and a single stamen from a floral cavity in the side of the body. It doesn't flower often as it reproduces primarily vegetatively. This is accomplished as the main plant or "mother frond" produces a "daughter frond" from one end.
Under the microscope at 40X but lit from the top, Wolffia looks like little jewels
Under the microscope at 40X and lit from the bottom, photo by Kit Knotts
The left mother/daughter frond near separation, the right just separated
Because the examples in these images were found in Florida, we presume them to be W. columbiana, native here. They also match the description and other images of W. columbiana. We are not certain as several references note that direct comparison with other Wolffia species is necessary to be sure of correct identification.
Wolffia seems not to be considered invasive and might actually have economic value. It has approximately the same percentage of protein as soy beans. Taking the suggestion of one of the web sites below and exploring the gourmet potential of Wolffia, we made this muffin using it. It was good!