The Big 4 in the U.S.

2. Butterhead lettuces have a rounded, head-like shape like Icebergs; but their heads are much more soft and loose. Their leaves are also usually a darker green, a sign that they contain more vitamins and healthful minerals.

The two most popular subtypes of Butterhead lettuce are Bibb, which looks like a big green cup, and Boston (shown here), which looks like an enormous flower with floppy dark green petals.

 

3. Looseleaf lettuces have no head at all. Instead, they have lots of frilly leaves joined at the base. Sometimes those leaves will be dark green; but sometimes they'll be deep reddish purple, as in the picture here.

 

4. Finally, Romaine lettuce has broad leaves with a strong white-ish spine running up their middle. This is the most bitter of the four types of lettuce. If you have ever eaten a Caesar salad, you have tasted Romaine lettuce.

Of these four types of lettuce, Romaine comes closest to what the ancient Egyptians grew on the banks of the Nile River 4,500 years ago.