arrow arum vs water plant

arrow arum and water plant both are nouns.

Word	Noun	Adjective	Verb	Adverb
arrow arum	Yes	No	No	No
water plant	Yes	No	No	No

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

arrow arum: an aquatic plant of the genus Peltandra; North 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 arrow arum include aquatic plant, hydrophyte, hydrophytic plant.

arrow arum (noun)	water plant (noun)
an aquatic plant of the genus Peltandra; North 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