spiraea vs shrub

spiraea and shrub both are nouns.

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

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

spiraea: 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 spiraea include bush.

spiraea (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