Hercules'-club vs shrub

Hercules'-club and shrub both are nouns.

Word	Noun	Adjective	Verb	Adverb
Hercules'-club	Yes	No	No	No
shrub	Yes	No	No	No

As nouns, shrub is a hypernym of Hercules'-club; that is, shrub is a word with a broader meaning than Hercules'-club:

Hercules'-club: small deciduous clump-forming tree or shrub of eastern United States
shrub: a low woody perennial plant usually having several major stems

Other hypernyms of Hercules'-club include bush.

Hercules'-club (noun)	shrub (noun)
densely spiny ornamental of southeastern United States and West Indies	a low woody perennial plant usually having several major stems
small deciduous clump-forming tree or shrub of eastern United States