herbage vs herbaceous plant

herbage and herbaceous plant both are nouns.

Word	Noun	Adjective	Verb	Adverb
herbage	Yes	No	No	No
herbaceous plant	Yes	No	No	No

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

herbage: succulent herbaceous vegetation of pastureland
herbaceous plant: a plant lacking a permanent woody stem; many are flowering garden plants or potherbs; some having medicinal properties; some are pests

Other hypernyms of herbage include herb.

herbage (noun)	herbaceous plant (noun)
succulent herbaceous vegetation of pastureland	a plant lacking a permanent woody stem; many are flowering garden plants or potherbs; some having medicinal properties; some are pests