yerba santa vs shrub

yerba santa and shrub both are nouns.

Word	Noun	Adjective	Verb	Adverb
yerba santa	Yes	No	No	No
shrub	Yes	No	No	No

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

yerba santa: viscid evergreen shrub of western United States with white to deep lilac flowers; the sticky aromatic leaves are used in treating bronchial and pulmonary illnesses
shrub: a low woody perennial plant usually having several major stems

Other hypernyms of yerba santa include bush.

yerba santa (noun)	shrub (noun)
viscid evergreen shrub of western United States with white to deep lilac flowers; the sticky aromatic leaves are used in treating bronchial and pulmonary illnesses	a low woody perennial plant usually having several major stems