More About Chinese Broccoli

Chinese broccoli — also known as kai-lan, gai-lan, and Chinese kale — is a leafy green vegetable closely related to thick-stemmed broccoli, cabbage, and Brussels sprouts. It has flat leaves, thick stems, and tiny florets.
Widely eaten in Chinese, Vietnamese, and Thai cuisine, Chinese broccoli has a slightly bitter and earthy taste, and is best after a quick steam or sauté, or in a stir-fry. It may prove tough to find Chinese broccoli in large grocery stores, so check your local Asian market, which is more likely to carry it.

Can They Be Used Interchangeably?

The short answer is yes, but there are a few caveats.
Because they vary in size and shape, certain swaps work better than others. If you're focused on florets, broccoli and Broccolini can easily be used interchangeably. If you're cooking with the broccoli stalk, Chinese broccoli also has a thick stem and makes a good substitute. And if the leafy greens are what you're after, broccoli rabe and Chinese broccoli can be used for one another. Do keep in mind that you may have to adjust the cook time to account for the swap.