spinach beet vs greens

spinach beet and greens both are nouns.

Word	Noun	Adjective	Verb	Adverb
spinach beet	Yes	No	No	No
greens	Yes	No	No	No

As nouns, greens is a hypernym of spinach beet; that is, greens is a word with a broader meaning than spinach beet:

spinach beet: long succulent whitish stalks with large green leaves
greens: any of various leafy plants or their leaves and stems eaten as vegetables

Other hypernyms of spinach beet include green, leafy vegetable.

spinach beet (noun)	greens (noun)
long succulent whitish stalks with large green leaves	any of various leafy plants or their leaves and stems eaten as vegetables
beet lacking swollen root; grown as a vegetable for its edible leaves and stalks