pepper grass vs cress plant

pepper grass and cress plant both are nouns.

Word	Noun	Adjective	Verb	Adverb
pepper grass	Yes	No	No	No
cress plant	Yes	No	No	No

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

pepper grass: annual herb used as salad green and garnish
cress plant: any of various plants of the family Cruciferae with edible leaves that have a pungent taste

Other hypernyms of pepper grass include cress.

pepper grass (noun)	cress plant (noun)
annual herb used as salad green and garnish	any of various plants of the family Cruciferae with edible leaves that have a pungent taste