wild celery vs water plant

wild celery and water plant both are nouns.

Word	Noun	Adjective	Verb	Adverb
wild celery	Yes	No	No	No
water plant	Yes	No	No	No

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

wild celery: submerged aquatic plant with ribbonlike leaves; Old World and Australia
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 wild celery include aquatic plant, hydrophyte, hydrophytic plant.

wild celery (noun)	water plant (noun)
submerged aquatic plant with ribbonlike leaves; Old World and Australia	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
herb of Europe and temperate Asia