mustard greens vs leaf mustard

mustard greens and leaf mustard both are nouns.

Word	Noun	Adjective	Verb	Adverb
mustard greens	Yes	No	No	No
leaf mustard	Yes	No	No	No

As nouns, mustard greens and leaf mustard are synonyms defined as:

Other synonyms of mustard greens include Indian mustard, mustard.

mustard greens (noun)	leaf mustard (noun)
leaves eaten as cooked greens	leaves eaten as cooked greens
	Asiatic mustard used as a potherb