head lettuce vs Lactuca sativa capitata

head lettuce and Lactuca sativa capitata both are nouns.

Word	Noun	Adjective	Verb	Adverb
head lettuce	Yes	No	No	No
Lactuca sativa capitata	Yes	No	No	No

As nouns, head lettuce and Lactuca sativa capitata are synonyms defined as:

head lettuce and Lactuca sativa capitata: distinguished by leaves arranged in a dense rosette that develop into a compact ball

head lettuce (noun)	Lactuca sativa capitata (noun)
distinguished by leaves arranged in a dense rosette that develop into a compact ball	distinguished by leaves arranged in a dense rosette that develop into a compact ball