How do kale and collards differ from head cabbage?

Kale, collards, and head cabbage are all agricultural forms of Brassica oleracea, but they differ primarily in their physical structure and how their leaves are arranged.1

While head cabbage is characterized by leaves that fold into compact, terminal heads, kale and collards are classified as loose-leafed or open-foliage forms (variety acephala).1

The specific differences include:

• Head Cabbage: Features leaves folded into compact, large terminal heads. These heads can range in shape from pointed to globular or flat and vary significantly in density and color.1
• Kale: Produces a rosette of elongated leaves that are typically wavy or frilled at the margins.2
• Collards: These resemble head cabbage more closely than kale does because their leaves are much broader and are not frilled. Unlike head cabbage, however, they do not form compact heads, instead growing as a rosette of leaves at the top of a main stem.3

In short, the primary distinction is that head cabbage develops a dense, folded head, whereas kale and collards maintain an open, loose-leafed growth habit.132