water lettuce vs pistia

water lettuce and pistia both are nouns.

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

As nouns, water lettuce and pistia are synonyms defined as:

water lettuce and pistia: pantropical floating plant forming a rosette of wedge-shaped leaves; a widespread weed in rivers and lakes

Other synonyms of water lettuce include Pistia stratiotes, Pistia stratoites, water cabbage.

water lettuce (noun)	pistia (noun)
pantropical floating plant forming a rosette of wedge-shaped leaves; a widespread weed in rivers and lakes	pantropical floating plant forming a rosette of wedge-shaped leaves; a widespread weed in rivers and lakes