water starwort vs water plant

water starwort and water plant both are nouns.

Word	Noun	Adjective	Verb	Adverb
water starwort	Yes	No	No	No
water plant	Yes	No	No	No

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

water starwort: any of several aquatic plants having a star-shaped rosette of floating leaves; America, Europe and Asia
water plant: 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 starwort include aquatic plant, hydrophyte, hydrophytic plant.

water starwort (noun)	water plant (noun)
any of several aquatic plants having a star-shaped rosette of floating leaves; America, Europe and Asia	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