purple saxifrage vs breakstone

purple saxifrage and breakstone both are nouns.

Word	Noun	Adjective	Verb	Adverb
purple saxifrage	Yes	No	No	No
breakstone	Yes	No	No	No

As nouns, breakstone is a hypernym of purple saxifrage; that is, breakstone is a word with a broader meaning than purple saxifrage:

purple saxifrage: plants forming dense cushions with bright reddish-lavender flowers; rocky areas of Europe and Asia and western North America
breakstone: any of various plants of the genus Saxifraga

Other hypernyms of purple saxifrage include rockfoil, saxifrage.

purple saxifrage (noun)	breakstone (noun)
plants forming dense cushions with bright reddish-lavender flowers; rocky areas of Europe and Asia and western North America	any of various plants of the genus Saxifraga