Nicotiana tabacum vs tobacco

Nicotiana tabacum and tobacco both are nouns.

Word	Noun	Adjective	Verb	Adverb
Nicotiana tabacum	Yes	No	No	No
tobacco	Yes	No	No	No

As nouns, tobacco is a hypernym of Nicotiana tabacum; that is, tobacco is a word with a broader meaning than Nicotiana tabacum:

Nicotiana tabacum: tall erect South American herb with large ovate leaves and terminal clusters of tubular white or pink flowers; cultivated for its leaves
tobacco: aromatic annual or perennial herbs and shrubs

Other hypernyms of Nicotiana tabacum include tobacco plant.

Nicotiana tabacum (noun)	tobacco (noun)
tall erect South American herb with large ovate leaves and terminal clusters of tubular white or pink flowers; cultivated for its leaves	leaves of the tobacco plant dried and prepared for smoking or ingestion
	aromatic annual or perennial herbs and shrubs