Clethra alnifolia vs shrub

Clethra alnifolia and shrub both are nouns.

Word	Noun	Adjective	Verb	Adverb
Clethra alnifolia	Yes	No	No	No
shrub	Yes	No	No	No

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

Clethra alnifolia: shrub of eastern and southern coastal United States having beautiful racemes of spice-scented white flowers
shrub: a low woody perennial plant usually having several major stems

Other hypernyms of Clethra alnifolia include bush.

Clethra alnifolia (noun)	shrub (noun)
shrub of eastern and southern coastal United States having beautiful racemes of spice-scented white flowers	a low woody perennial plant usually having several major stems