water milfoil vs hydrophyte

water milfoil and hydrophyte both are nouns.

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

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

water milfoil: an aquatic plant of the genus Myriophyllum having feathery underwater leaves and small inconspicuous flowers
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 milfoil include aquatic plant, hydrophytic plant, water plant.

water milfoil (noun)	hydrophyte (noun)
an aquatic plant of the genus Myriophyllum having feathery underwater leaves and small inconspicuous flowers	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