duckweed

Etymology

From duck + weed. Supposedly so-named for often being consumed by ducks and other waterfowl. Compare Middle English dokemete (“duckweed”, literally “duck-food”).

noun

1. Any of several reduced floating aquatic plants in the subfamily Lemnoideae of the family Araceae.
   But his face was a face of such happiness that, had you seen it, you would have understood indeed how that he had died happy, never knowing that cool and streaming silver for the duckweed in the pond. 1909, H. G. Wells, The Beautiful Suit