Romaine lettuce is the term more often used in the USA to describe a Cos lettuce. Typically it 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.
This type of lettuce is extremely popular due to the creation of the Caesar Salad. There are many interpretations of this recipe, but it most definitely should start with a cos.
They’re shaped like green cabbages, but the leaves are deep green and deeply crinkled. Their flavor is mild and earhty, and the leaves are tender even when raw. Heads should be compact and tight, but will have a little more give to them because of the wrinkled leaves. It can be sliced thinly in soups and stir-fries.