The varieties of 'radicchio' are named after the Italian regions where they originate: the most ubiquitous variety in the United States is 'radicchio' di Chioggia, which is maroon, round, and about the size of a grapefruit.
Other varieties include 'Tardivo', and the white-colored 'radicchio di Castelfranco', both of which resemble flowers and are only available in the winter months, as well as 'Gorizia' (also known as "Rosa di Gorizia"), 'Trieste' (Cicoria zuccherina or Biondissima) and 'Witloof/Bruxelles' (also known as Belgian endive, and "chicon/endive" in French).