rupestral plant vs rock plant

rupestral plant and rock plant both are nouns.

Word	Noun	Adjective	Verb	Adverb
rupestral plant	Yes	No	No	No
rock plant	Yes	No	No	No

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

rupestral plant: plants growing among rocks
rock plant: plant that grows on or among rocks or is suitable for a rock garden

rupestral plant (noun)	rock plant (noun)
plants growing among rocks	plant that grows on or among rocks or is suitable for a rock garden