Examples from literature

• But in this flower-pot, sunk so as to be in the water, and yet so that the rim may prevent it from spreading and coating the entire tank with green, is the strangest of all, actually duckweed. 
• I recommend all country folk who come up to town in summer time to run down here just to see duckweed cultivated once in their lives. 
• Many of the craters half-filled with water already had duckweed growing. 
• There is a large pond in the midst of the garden, covered with duckweed, and full of beautiful gold and silver fish of many kinds.