The origins of broccoli rabe (brassica rapa) can be traced back to China as well as the Mediterranean. Given this vegetable is more closely related to a turnip than to broccoli the heritage is more likely Chinese given it is the home to literally hundreds of similar greens.
The U.S. history is quite well documented. Broccoli was brought to the U.S. in 1927 by the D'Arrigo brothers, Italian immigrants. One of the brothers found the plant growing wild all over California and recognized from his homeland. He began breeding the plant in the 1930's and the planted has been marketed here ever since that time.
Brassica rapa - This is a nice, fast growing, cool weather plant. It matures in about 40 to 60 days. The best time to grow it is in early spring and also in fall. Plants grow to 12 inches tall. If grown in too much heat the plants will bolt (go to seed) too quickly.
Pick the greens after the florets form but before the florets begin to open. Cut the plants at the ground level, or where the stem begins to get thick and toughen. If you harvest correctly, and the weather remains cool, you can expect a second and possibly third cutting from each plant.
If you are growing your own plants, then it is best to harvest right before your meal. If you need to store it, seal it in a plastic bag and refrigerate it in your vegetable crisper for up to 5 days.