viper's grass vs genus Scorzonera

viper's grass and genus Scorzonera both are nouns.

Word	Noun	Adjective	Verb	Adverb
viper's grass	Yes	No	No	No
genus Scorzonera	Yes	No	No	No

viper's grass (noun)	genus Scorzonera (noun)
perennial south European herb having narrow entire leaves and solitary yellow flower heads and long black edible roots shaped like carrots	genus of narrow-leaved European herbs