Russian tumbleweed vs shrub

Russian tumbleweed and shrub both are nouns.

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

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

Russian tumbleweed: 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 tumbleweed include bush.

Russian tumbleweed (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