mountain rimu vs shrub

mountain rimu and shrub both are nouns.

Word	Noun	Adjective	Verb	Adverb
mountain rimu	Yes	No	No	No
shrub	Yes	No	No	No

As nouns, shrub is a hypernym of mountain rimu; that is, shrub is a word with a broader meaning than mountain rimu:

mountain rimu: low-growing to prostrate shrub with slender trailing branches; New Zealand
shrub: a low woody perennial plant usually having several major stems

Other hypernyms of mountain rimu include bush.

mountain rimu (noun)	shrub (noun)
low-growing to prostrate shrub with slender trailing branches; New Zealand	a low woody perennial plant usually having several major stems