showy sunflower vs helianthus

showy sunflower and helianthus both are nouns.

Word	Noun	Adjective	Verb	Adverb
showy sunflower	Yes	No	No	No
helianthus	Yes	No	No	No

As nouns, helianthus is a hypernym of showy sunflower; that is, helianthus is a word with a broader meaning than showy sunflower:

showy sunflower: tall rough-leaved perennial with a few large flower heads; central United States
helianthus: any plant of the genus Helianthus having large flower heads with dark disk florets and showy yellow rays

Other hypernyms of showy sunflower include sunflower.

showy sunflower (noun)	helianthus (noun)
tall rough-leaved perennial with a few large flower heads; central United States	any plant of the genus Helianthus having large flower heads with dark disk florets and showy yellow rays