No- they are not small cabbages, but they are related! If you remember way back to biology class, there is an order to taxonomy rank for plants. You can refresh your memory here. Basically, the family is more broad of a category than species. How that sugars out for Brussels Sprouts is the following: Brassica Family: Brussels Sprouts are a cool season biennial in the Brassicaceae family which is also known as the mustards. This is a huge family that includes some of our favorite healthy veggies like turnips and mustard greens.  Brassica Oleracea Species: Within the Brassica family, Brussels sprouts falls in the Brassica Oleracea Species. There are several varieties of brassica vegetables in this species which also include: cauliflower, cabbage,  collards, kale, broccoli, and kohlrabi. {Source.}