wheat-grass vs wheatgrass

wheat-grass and wheatgrass both are nouns.

Word	Noun	Adjective	Verb	Adverb
wheat-grass	Yes	No	No	No
wheatgrass	Yes	No	No	No

As nouns, wheat-grass and wheatgrass are synonyms defined as:

wheat-grass (noun)	wheatgrass (noun)
a grass of the genus Agropyron	a grass of the genus Agropyron