Broccolini, often mistakenly thought to be 'young' or 'baby' broccoli is a green vegetable that is a cross between Broccoli and Kai-Lan - a Chinese Kale.
It has small green florets with little yellow flowers, similar to broccoli and long, thin stalks. I found it to be a sweeter version of Broccoli, with the occasional hint of kale-like bitterness, and the stem tasted a lot like asparagus.
Broccolini is rich in fiber (like most other veggies, duh!) and is rich in Vitamins A, B9 (folic acid) and C. It is also a rich source of Calcium, potassium and iron. The whole plant is edible and typically requires very little cook time, so this is a great vegetable for stir fries.