rock purslane vs herb

rock purslane and herb both are nouns.

Word	Noun	Adjective	Verb	Adverb
rock purslane	Yes	No	No	No
herb	Yes	No	No	No

As nouns, herb is a hypernym of rock purslane; that is, herb is a word with a broader meaning than rock purslane:

rock purslane: a plant of the genus Calandrinia
herb: a plant lacking a permanent woody stem; many are flowering garden plants or potherbs; some having medicinal properties; some are pests

Other hypernyms of rock purslane include herbaceous plant.

rock purslane (noun)	herb (noun)
a plant of the genus Calandrinia	aromatic potherb used in cookery for its savory qualities
	a plant lacking a permanent woody stem; many are flowering garden plants or potherbs; some having medicinal properties; some are pests