pampas grass vs genus Cortaderia

pampas grass and genus Cortaderia both are nouns.

Word	Noun	Adjective	Verb	Adverb
pampas grass	Yes	No	No	No
genus Cortaderia	Yes	No	No	No

pampas grass (noun)	genus Cortaderia (noun)
tall perennial grass of Pampas of South America having silvery plumes and growing in large dense clumps	tall ornamental grasses of South America and New Zealand and New Guinea: pampas grass