spinach beet vs Beta vulgaris

spinach beet and Beta vulgaris both are nouns.

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

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

spinach 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 spinach beet include beet, common beet.

spinach 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