water lettuce vs hydrophyte

water lettuce and hydrophyte both are nouns.

Word	Noun	Adjective	Verb	Adverb
water lettuce	Yes	No	No	No
hydrophyte	Yes	No	No	No

As nouns, hydrophyte is a hypernym of water lettuce; that is, hydrophyte is a word with a broader meaning than water lettuce:

water lettuce: pantropical floating plant forming a rosette of wedge-shaped leaves; a widespread weed in rivers and lakes
hydrophyte: a plant that grows partly or wholly in water whether rooted in the mud, as a lotus, or floating without anchorage, as the water hyacinth

Other hypernyms of water lettuce include aquatic plant, hydrophytic plant, water plant.

water lettuce (noun)	hydrophyte (noun)
pantropical floating plant forming a rosette of wedge-shaped leaves; a widespread weed in rivers and lakes	a plant that grows partly or wholly in water whether rooted in the mud, as a lotus, or floating without anchorage, as the water hyacinth