Zostera marina vs hydrophyte

Zostera marina and hydrophyte both are nouns.

Word	Noun	Adjective	Verb	Adverb
Zostera marina	Yes	No	No	No
hydrophyte	Yes	No	No	No

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

Zostera marina: submerged marine plant with very long narrow leaves found in abundance along North Atlantic coasts
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 Zostera marina include aquatic plant, hydrophytic plant, water plant.

Zostera marina (noun)	hydrophyte (noun)
submerged marine plant with very long narrow leaves found in abundance along North Atlantic coasts	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