smut grass vs genus Sporobolus

smut grass and genus Sporobolus both are nouns.

Word	Noun	Adjective	Verb	Adverb
smut grass	Yes	No	No	No
genus Sporobolus	Yes	No	No	No

smut grass (noun)	genus Sporobolus (noun)
grass native to West Indies but common in southern United States having tufted wiry stems often infested with a dark fungus	cosmopolitan annual and perennial grasses (as dropseed or rush grass)