water speedwell vs water plant

water speedwell and water plant both are nouns.

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

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

water speedwell: plant of wet places in Eurasia and America
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 speedwell include aquatic plant, hydrophyte, hydrophytic plant.

water speedwell (noun)	water plant (noun)
plant of wet places in Eurasia and America	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