Ornamental kale is part of the mustard family (genus brassicaceae) and is a very close relative to cabbage, cauliflower, broccoli and brussels sprouts. Even though it is related to edible vegetables, ornamental kale is for decorative purposes only (don't eat it!).
You'll find that most flower farmers and designers call ornamental kale by its genus, “brassica,” and other folks will simply call it “cabbage.” All names are acceptable and interchangeable.
Whatever you choose to call it, brassica isn't a new crop to the flower industry, and in the horticulture world it is very established. What is new about this crop; is that now flower designers and consumers can get this traditional cool weather crop year-round. The colors that are most in demand are the white, lavender and purple.
In order for the kale to "color up" you need cool temperatures at night, which makes it an excellent fall and winter crop. However, there are plenty of cool-weather locations to farm brassica year-round. For example, if farming ornamental kale near the coast, summertime often brings cool, foggy morning AND evenings, which make for excellent brassica growing conditions.
Brassica’s current widespread popularity can be attributed to its natural, “Farmer’s Market” type feel. People are loving simple arrangements that look like the elements were gathered from a backyard garden or a roadside stand. Brassica has that warm, earthy feel, as well as a the popular “back to the land” element, with bulk, lovely color, and intense texture of a more upscale botanical.