witchgrass vs wheatgrass

witchgrass and wheatgrass both are nouns.

Word	Noun	Adjective	Verb	Adverb
witchgrass	Yes	No	No	No
wheatgrass	Yes	No	No	No

As nouns, wheatgrass is a hypernym of witchgrass; that is, wheatgrass is a word with a broader meaning than witchgrass:

witchgrass: European grass spreading rapidly by creeping rhizomes; naturalized in North America as a weed
wheatgrass: a grass of the genus Agropyron

Other hypernyms of witchgrass include wheat-grass.

witchgrass (noun)	wheatgrass (noun)
North American grass with slender brushy panicles; often a weed on cultivated land	a grass of the genus Agropyron
European grass spreading rapidly by creeping rhizomes; naturalized in North America as a weed