petunia vs flower

petunia and flower both are nouns.

Word	Noun	Adjective	Verb	Adverb
petunia	Yes	No	No	No
flower	Yes	No	Yes	No

As nouns, flower is a hypernym of petunia; that is, flower is a word with a broader meaning than petunia:

petunia (noun)	flower (noun)
any of numerous tropical herbs having fluted funnel-shaped flowers	a plant cultivated for its blooms or blossoms
	reproductive organ of angiosperm plants especially one having showy or colorful parts
	the period of greatest prosperity or productivity

petunia (verb)	flower (verb)
	produce or yield flowers