purple-stemmed aster vs aster

purple-stemmed aster and aster both are nouns.

Word	Noun	Adjective	Verb	Adverb
purple-stemmed aster	Yes	No	No	No
aster	Yes	No	No	No

As nouns, aster is a hypernym of purple-stemmed aster; that is, aster is a word with a broader meaning than purple-stemmed aster:

purple-stemmed aster: a variety of aster (Symphyotrichum puniceum)
aster: any of various chiefly fall-blooming herbs of the genus Aster with showy daisylike flowers

purple-stemmed aster (noun)	aster (noun)
a variety of aster (Symphyotrichum puniceum)	star-shaped structure formed in the cytoplasm of a cell having fibers like rays that surround the centrosome during mitosis
	any of various chiefly fall-blooming herbs of the genus Aster with showy daisylike flowers