Pistia stratiotes

Water lettuce is a free-floating freshwater tropical or subtropical plant that spreads along the surface of the water. This is a very undemanding aquatic plant and probably one of the most productive freshwater plants in the world. First discovered from the river Nile in Africa it is now cultivated artificially around the globe. True to its name, Water lettuce resembles the appearance of the edible lettuce plant used in salads worldwide. Its size depends on the environment it is grown in, which is why they get very large in ponds and stay pretty small in small aquariums.

Image credits: GreenDNA, Himadri aquatics