alligator grass vs alligator weed

alligator grass and alligator weed both are nouns.

Word	Noun	Adjective	Verb	Adverb
alligator grass	Yes	No	No	No
alligator weed	Yes	No	No	No

As nouns, alligator grass and alligator weed are synonyms defined as:

alligator grass and alligator weed: prolific South American aquatic weed having grasslike leaves and short spikes of white flowers; clogs waterways with dense floating masses

Other synonyms of alligator grass include Alternanthera philoxeroides.

alligator grass (noun)	alligator weed (noun)
prolific South American aquatic weed having grasslike leaves and short spikes of white flowers; clogs waterways with dense floating masses	prolific South American aquatic weed having grasslike leaves and short spikes of white flowers; clogs waterways with dense floating masses