Amaranthus albus vs amaranth

Amaranthus albus and amaranth both are nouns.

Word	Noun	Adjective	Verb	Adverb
Amaranthus albus	Yes	No	No	No
amaranth	Yes	No	No	No

As nouns, amaranth is a hypernym of Amaranthus albus; that is, amaranth is a word with a broader meaning than Amaranthus albus:

Amaranthus albus: bushy plant of western United States
amaranth: any of various plants of the genus Amaranthus having dense plumes of green or red flowers; often cultivated for food

Amaranthus albus (noun)	amaranth (noun)
bushy plant of western United States	any of various plants of the genus Amaranthus having dense plumes of green or red flowers; often cultivated for food
	seed of amaranth plants used as a native cereal in Central and South America