quackgrass vs quack grass

quackgrass and quack grass both are nouns.

Word	Noun	Adjective	Verb	Adverb
quackgrass	Yes	No	No	No
quack grass	Yes	No	No	No

As nouns, quackgrass and quack grass are synonyms defined as:

quackgrass and quack grass: European grass spreading rapidly by creeping rhizomes; naturalized in North America as a weed

Other synonyms of quackgrass include Agropyron repens, couch grass, dog grass, quick grass, witch grass, witchgrass.

quackgrass (noun)	quack grass (noun)
European grass spreading rapidly by creeping rhizomes; naturalized in North America as a weed	European grass spreading rapidly by creeping rhizomes; naturalized in North America as a weed