pearlweed vs ground cover

pearlweed and ground cover both are nouns.

Word	Noun	Adjective	Verb	Adverb
pearlweed	Yes	No	No	No
ground cover	Yes	No	No	No

As nouns, ground cover is a hypernym of pearlweed; that is, ground cover is a word with a broader meaning than pearlweed:

pearlweed: any of various low-growing plants of the genus Sagina having small spherical flowers resembling pearls
ground cover: low-growing plants planted in deep shade or on a steep slope where turf is difficult to grow

Other hypernyms of pearlweed include groundcover.

pearlweed (noun)	ground cover (noun)
any of various low-growing plants of the genus Sagina having small spherical flowers resembling pearls	small plants other than saplings growing on a forest floor
	low-growing plants planted in deep shade or on a steep slope where turf is difficult to grow