leaf beet vs Beta vulgaris

leaf beet and Beta vulgaris both are nouns.

Word	Noun	Adjective	Verb	Adverb
leaf beet	Yes	No	No	No
Beta vulgaris	Yes	No	No	No

As nouns, Beta vulgaris is a hypernym of leaf beet; that is, Beta vulgaris is a word with a broader meaning than leaf beet:

leaf beet: beet lacking swollen root; grown as a vegetable for its edible leaves and stalks
Beta vulgaris: biennial Eurasian plant usually having a swollen edible root; widely cultivated as a food crop

Other hypernyms of leaf beet include beet, common beet.

leaf beet (noun)	Beta vulgaris (noun)
long succulent whitish stalks with large green leaves	biennial Eurasian plant usually having a swollen edible root; widely cultivated as a food crop
beet lacking swollen root; grown as a vegetable for its edible leaves and stalks