Received these water ferns (Azolla microphylla) from a friend...
Fast growing like... weeds (what else :D)
Excellent food value. The finches and chicken loves them. Only fear are water borne pathogens. So I soak them in a home made chlorinated water and rinse with tap water before feeding.
How to make food safe disinfectant? Using regular bleach (usually 5.25% available in local stores), and the services of an online calculator, 4ml added to 1L of water will get a solution that is 200ppm (parts per million), which is safe for consumption. Anyway I still rinse them off before feeding the birds.
The below is an excellent documentary on Azolla...