spirea vs shrub

spirea and shrub both are nouns.

Word	Noun	Adjective	Verb	Adverb
spirea	Yes	No	No	No
shrub	Yes	No	No	No

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

spirea: any rosaceous plant of the genus Spiraea; has sprays of small white or pink flowers
shrub: a low woody perennial plant usually having several major stems

Other hypernyms of spirea include bush.

spirea (noun)	shrub (noun)
any rosaceous plant of the genus Spiraea; has sprays of small white or pink flowers	a low woody perennial plant usually having several major stems
a Japanese shrub that resembles members of the genus Spiraea; widely cultivated in many varieties for its dense panicles of flowers in many colors; often forced by florists for Easter blooming