Japanese radish vs radish plant

Japanese radish and radish plant both are nouns.

Word	Noun	Adjective	Verb	Adverb
Japanese radish	Yes	No	No	No
radish plant	Yes	No	No	No

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

Japanese radish: radish of Japan with a long hard durable root eaten raw or cooked
radish plant: a cruciferous plant of the genus Raphanus having a pungent edible root

Other hypernyms of Japanese radish include radish.

Japanese radish (noun)	radish plant (noun)
radish of Japan with a long hard durable root eaten raw or cooked	a cruciferous plant of the genus Raphanus having a pungent edible root