Typically Romaine is a tall lettuce with long slender leaves and at maturity forms an elongated cupped 'heart'. The leaves have quite a prominent and thicker rib through the centre, are generally more robust with a unique crisp taste that differentiates it from other lettuce. When grown to maturity, the upper tips of the leaves close to form a heart, which consequentially excludes light, colouring the internals to more of a blonde green. It is these paler leaves that are most tasty, tender and desirable.
Romaine lettuce is an excellent source of dietary fiber, vitamins A, C, and K, thiamin, folate, iron, potassium, and manganese. It is also a good source of riboflavin, vitamin B6, calcium, magnesium, phosphorus, and copper.