Brassica oleracea Capitata Group.
The tight heads of leaves are not seen in the wild but are a cultivated trait.
They are derived from the wild cabbage Brassica oleracea.
Leaves along the stem curve inwards with increasing tightness compressing the newer ones
underneath into a dense head.
They are harvested in the first year before flowers appear.
Examples of the many types of cabbage include:
Brassica oleracea var. capitata f. alba.
White cabbage has smooth pale green leaves packed into a roundish head.
Brassica oleracea var. capitata f. rubra.
The Red cabbage has a compact head of purple leaves.
Brassica oleracea var. capitata f. sabauda.
Savoy cabbages have looser heads of very puckered green or red leaves.
Brassica oleracea var. capitata f. acuta.
Cone cabbage has a pointed head.