cowpea plant vs cowpea

cowpea plant and cowpea both are nouns.

Word	Noun	Adjective	Verb	Adverb
cowpea plant	Yes	No	No	No
cowpea	Yes	No	No	No

As nouns, cowpea plant and cowpea are synonyms defined as:

cowpea plant and cowpea: sprawling Old World annual cultivated especially in southern United States for food and forage and green manure

Other synonyms of cowpea plant include black-eyed pea, Vigna sinensis, Vigna unguiculata.

cowpea plant (noun)	cowpea (noun)
sprawling Old World annual cultivated especially in southern United States for food and forage and green manure	eaten fresh as shell beans or dried
	sprawling Old World annual cultivated especially in southern United States for food and forage and green manure
	fruit or seed of the cowpea plant