blue toadflax vs devil's flax

blue toadflax and devil's flax both are nouns.

Word	Noun	Adjective	Verb	Adverb
blue toadflax	Yes	No	No	No
devil's flax	Yes	No	No	No

As nouns, devil's flax is a hypernym of blue toadflax; that is, devil's flax is a word with a broader meaning than blue toadflax:

blue toadflax: North American plant having racemes of blue-violet flowers
devil's flax: common European perennial having showy yellow and orange flowers; a naturalized weed in North America

Other hypernyms of blue toadflax include butter-and-eggs, Linaria vulgaris, toadflax, wild snapdragon.

blue toadflax (noun)	devil's flax (noun)
North American plant having racemes of blue-violet flowers	common European perennial having showy yellow and orange flowers; a naturalized weed in North America