vascular plant vs herb

vascular plant and herb both are nouns.

Word	Noun	Adjective	Verb	Adverb
vascular plant	Yes	No	No	No
herb	Yes	No	No	No

As nouns, herb is a hyponym of vascular plant; that is, herb is a word with a more specific, narrower meaning than vascular plant:

vascular plant: green plant having a vascular system: ferns, gymnosperms, angiosperms
herb: a plant lacking a permanent woody stem; many are flowering garden plants or potherbs; some having medicinal properties; some are pests

vascular plant (noun)	herb (noun)
green plant having a vascular system: ferns, gymnosperms, angiosperms	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