Ornamental cabbage and kale look and grow very much like their close relatives, the edible cabbages and kales. Although they're categorized as the same species (Brassica oleracea) as the edible varieties, these ornamental cultivars have been bred for looks, not flavor. They are slightly bitter, though are often used as a garnish. Their leaves form rosettes of purple, rose, and creamy white colors, making them look more like large flowers than vegetables. In the horticultural trade, the varieties with smooth leaf margins and broad, flat leaves are generally referred to as flowering cabbages, while those with serrated or fringed leaf margins are considered flowering kales. (Technically, both are kales, because kale has leaves that form rosettes while a true cabbage has leaves that form a head.)
Officially, ornamental cabbage and kale are cool-season biennials. This means they grow their vegetative leaves the first year and then send up flowers the second year, producing seeds before the plant dies. However, these fast-growing plants are usually grown as annuals for their showy foliage, planted from nursery starts in the fall or early spring, then removed from the garden after the seasonal display is concluded.