watercress vs cress plant

watercress and cress plant both are nouns.

Word	Noun	Adjective	Verb	Adverb
watercress	Yes	Yes	No	No
cress plant	Yes	No	No	No

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

watercress: any of several water-loving cresses
cress plant: any of various plants of the family Cruciferae with edible leaves that have a pungent taste

Other hypernyms of watercress include cress.

watercress (noun)	cress plant (noun)
cresses that grow in clear ponds and streams	any of various plants of the family Cruciferae with edible leaves that have a pungent taste
any of several water-loving cresses

watercress (adjective)	cress plant (adjective)
of a moderate yellow-green color that is greener and deeper than moss green and yellower and darker than pea green