pearlweed vs groundcover

pearlweed and groundcover both are nouns.

Word	Noun	Adjective	Verb	Adverb
pearlweed	Yes	No	No	No
groundcover	Yes	No	No	No

As nouns, groundcover is a hypernym of pearlweed; that is, groundcover 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
groundcover: low-growing plants planted in deep shade or on a steep slope where turf is difficult to grow

Other hypernyms of pearlweed include ground cover.

pearlweed (noun)	groundcover (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