duckweed as food
Duckweed, also known as water lentils, floats a lot on ponds, but has recently also been grown for consumption. The green plant contains a lot of protein and would therefore be a good substitute for meat or soy. The taste, which seemingly resembles watercress, will take some getting used to, but in China people already eat it abundantly. The easy growth of the plant and the fact that there are no negative health effects so far, make the water lentils an interesting new foodstuff.
Update: Duckweed also appears suitable as basis for dairy alternatives