Although calabrese is in many ways similar to broccoli, it is usually considered as a separate vegetable. Its origins are the same: it originated in the countries of the Eastern Mediterranean coast (and Italy); before moving to the rest of Europe. It is sometimes known as Italian broccoli or American broccoli. (Romanesco is usually bracketed with calabrese).
Unlike broccoli, Calabrese is quick growing but not very hardy, and it is grown so that the edible heads, which are much larger than those of broccoli, are produced in late summer and autumn. Calabrese forms a large central head, rather like a louse cauliflower, and when this is picked, side shoots develop, each carrying a slightly smaller head. Not all varieties are capable of producing side shoots however, and these varieties are finished once the main head is picked. The color is different from broccoli in that it has a blue-green tinge. Another major difference to broccoli is that it is important that growth should not be checked so it is sown where it is to grow and not transplanted.
Romanesco is similar to calabrese and is, in factt, often listed as a variety of calabrese. The main difference is that it is hardier and can be grown to produce heads from late autumn into early winter, covering at least part of the cap between calabrese and broccoli. Unlike calabrese and broccoli, romanesco only produces a single head and is then finished. The shape of the head is also different. It is distinctly conical-shaped, with little erruptions over the surface, creating further pinnacles. It is said to be attractive, with yellowish, lime-green buds.