There are different varieties of radicchio from the large round lettuce-shaped radicchio chioggia to the slender stalky treviso. Most common in the UK is red chicory, an endive-shaped small radicchio. Castelfranco is a white, round radicchio and worth seeking out. Radicchio is in season during the autumn and spring, but is often farmed over the winter too, making it a fantastic winter salad option.