wool grass vs genus Erianthus

wool grass and genus Erianthus both are nouns.

Word	Noun	Adjective	Verb	Adverb
wool grass	Yes	No	No	No
genus Erianthus	Yes	No	No	No

wool grass (noun)	genus Erianthus (noun)
grass often cultivated for its long white-ribbed leaves and large plumes resembling those of pampas grass	genus of reedlike grasses having spikes crowded in a panicle covered with long silky hairs
sedge of eastern North America having numerous clustered woolly spikelets