white turnip vs turnip plant

white turnip and turnip plant both are nouns.

Word	Noun	Adjective	Verb	Adverb
white turnip	Yes	No	No	No
turnip plant	Yes	No	No	No

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

white turnip: widely cultivated plant having a large fleshy edible white or yellow root
turnip plant: any of several widely cultivated plants having edible roots

white turnip (noun)	turnip plant (noun)
white root of a turnip plant	any of several widely cultivated plants having edible roots
widely cultivated plant having a large fleshy edible white or yellow root