There are several varieties of radicchio, but the two most widely available in the United States are Verona and Treviso. Radicchio di Verona has burgundy-red leaves with white ribs and grows in small, loose heads similar to butterhead lettuce. In contrast, the leaves of radicchio di Treviso are narrow and pointed and form tighter, more tapered heads. They also have white ribs, but can range in color from pink to dark red. Other radicchio varieties have variegated or speckled leaves in vibrant shades of pink, red and green.
All radicchios have tender but firm leaves with a slightly bitter flavor.
Although radicchio is available year-round, the vegetable's peak season is midwinter to early spring. Given its hardy nature, unwashed radicchio can be wrapped in plastic and stored in a refrigerator up to a week. With the widespread availability of the vegetable in supermarkets today, it may be hard to remember that radicchio was considered exotic and hard to find in the U.S. until the mid-1990s. The vegetable has long been popular in Italy, where it was first cultivated in the sixteenth century. And, although farmers on the West Coast would argue the point, most of the finest radicchio sold in the U.S. today is still imported from Italy or southern France.