cotton rose vs hibiscus

cotton rose and hibiscus both are nouns.

Word	Noun	Adjective	Verb	Adverb
cotton rose	Yes	No	No	No
hibiscus	Yes	No	No	No

As nouns, hibiscus is a hypernym of cotton rose; that is, hibiscus is a word with a broader meaning than cotton rose:

cotton rose: Chinese shrub or small tree having white or pink flowers becoming deep red at night; widely cultivated; naturalized in southeastern United States
hibiscus: any plant of the genus Hibiscus

cotton rose (noun)	hibiscus (noun)
any plant of the genus Filago having capitate clusters of small woolly flower heads	any plant of the genus Hibiscus
Chinese shrub or small tree having white or pink flowers becoming deep red at night; widely cultivated; naturalized in southeastern United States