A moderately bitter chicory that looks like a head of lettuce in the field. In Italy they have also an all white version. In North America the spherical red and white Radicchio di Chioggia variety is most common, but an elongated red and white Treviso variety that looks like a big red Belgian endive is also seen.
This is a fairly expensive lettuce because of the production method. In the field they are green. To make them purely red and white they are pulled from the ground and put in water in a dark room until the chlorophyll has faded from lack of light. This is labor and capital intensive and a lot of outer leaves are lost in the process, resulting in the high price. It is generally sold as heads 3-1/2 to 4-1/2 inches diameter weighing 9 to 10 ounces. Photo by Paolo Ciarlantini licensed under Creative Commons Attribution-ShareAlike v2.5 Generic .
More on Lettuce & Chicory
Two forms are sold, the spherical being more common. They are essentially identical except for shape.