Swiss chard vs greens

Swiss chard and greens both are nouns.

Word	Noun	Adjective	Verb	Adverb
Swiss chard	Yes	No	No	No
greens	Yes	No	No	No

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

Swiss chard: 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 Swiss chard include green, leafy vegetable.

Swiss chard (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