Romaine lettuce is a type of salad lettuce. It comes from the same plant family as other types of lettuce.
The name romaine suggests that the lettuce might have originated in Rome. It also grows well in the Mediterranean climate.
Romaine lettuce leaves are long and taper toward the root of the lettuce. The upper part of the leaves is a deeper green color and more flimsy than the lower leaves.
Toward the bottom of the lettuce, the leaves become sturdier and have thick, white ribs that contain a slightly bitter fluid. This gives romaine lettuce its distinctive taste.
The amount of this bitter fluid increases farther down the stalk. Some people throw away the thickest part of the leaves to avoid this bitterness.