ornamental vs plant life

ornamental and plant life both are nouns.

Word	Noun	Adjective	Verb	Adverb
ornamental	Yes	Yes	No	No
plant life	Yes	No	No	No

As nouns, plant life is a hypernym of ornamental; that is, plant life is a word with a broader meaning than ornamental:

Other hypernyms of ornamental include flora, plant.

ornamental (noun)	plant life (noun)
any plant grown for its beauty or ornamental value	(botany) a living organism lacking the power of locomotion

ornamental (adjective)	plant life (adjective)
serving an esthetic rather than a useful purpose