plant kingdom vs kingdom Plantae

plant kingdom and kingdom Plantae both are nouns.

Word	Noun	Adjective	Verb	Adverb
plant kingdom	Yes	No	No	No
kingdom Plantae	Yes	No	No	No

As nouns, plant kingdom and kingdom Plantae are synonyms defined as:

plant kingdom and kingdom Plantae: (botany) the taxonomic kingdom comprising all living or extinct plants

Other synonyms of plant kingdom include Plantae.

plant kingdom (noun)	kingdom Plantae (noun)
(botany) the taxonomic kingdom comprising all living or extinct plants	(botany) the taxonomic kingdom comprising all living or extinct plants