romaine lettuce vs Lactuca sativa longifolia

romaine lettuce and Lactuca sativa longifolia both are nouns.

Word	Noun	Adjective	Verb	Adverb
romaine lettuce	Yes	No	No	No
Lactuca sativa longifolia	Yes	No	No	No

As nouns, romaine lettuce and Lactuca sativa longifolia are synonyms defined as:

romaine lettuce and Lactuca sativa longifolia: lettuce with long dark-green spoon-shaped leaves

Other synonyms of romaine lettuce include cos lettuce.

romaine lettuce (noun)	Lactuca sativa longifolia (noun)
lettuce with long dark-green leaves in a loosely packed elongated head	lettuce with long dark-green spoon-shaped leaves
lettuce with long dark-green spoon-shaped leaves