Russian thistle vs shrub

Russian thistle and shrub both are nouns.

Word	Noun	Adjective	Verb	Adverb
Russian thistle	Yes	No	No	No
shrub	Yes	No	No	No

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

Russian thistle: prickly bushy Eurasian plant; a troublesome weed in central and western United States
shrub: a low woody perennial plant usually having several major stems

Other hypernyms of Russian thistle include bush.

Russian thistle (noun)	shrub (noun)
prickly bushy Eurasian plant; a troublesome weed in central and western United States	a low woody perennial plant usually having several major stems