sweet fern vs shrub

sweet fern and shrub both are nouns.

Word	Noun	Adjective	Verb	Adverb
sweet fern	Yes	No	No	No
shrub	Yes	No	No	No

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

sweet fern: deciduous shrub of eastern North America with sweet scented fernlike leaves and tiny white flowers
shrub: a low woody perennial plant usually having several major stems

Other hypernyms of sweet fern include bush.

sweet fern (noun)	shrub (noun)
deciduous shrub of eastern North America with sweet scented fernlike leaves and tiny white flowers	a low woody perennial plant usually having several major stems
mat-forming lithophytic or terrestrial fern with creeping rootstocks and large pinnatifid fronds found throughout North America and Europe and Africa and east Asia