duckweed

duck +‎ weed

duckweed (countable and uncountable, plural duckweeds or duckweed)

1. Any of several reduced floating aquatic plants in the subfamily Lemnoideae of the family Araceae.
   • 1909, H. G. Wells, The Beautiful Suit

     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.