The Brassica genus contains some of the world’s most familiar and agriculturally important vegetables, including cabbage, broccoli, and turnip. Belonging to the mustard family, this group has been cultivated for thousands of years. The original wild Brassica was an unassuming perennial native to the rocky coastlines of Europe. Through intentional selection, this single genus has been transformed into a visually diverse collection of food crops, emphasizing the development of leaves, stems, roots, or flowers.
Shared Visual Characteristics of the Brassica Genus
Despite the visual differences between cultivars, all Brassica plants share unifying botanical features. Their flowers are the most recognizable trait, consistently displaying four petals arranged in a cross shape. These yellow or sometimes white flowers typically develop in clusters atop a stem. The foliage often appears waxy and bluish-green due to a natural coating, and leaves are generally simple and arranged alternately along the stem. After pollination, the flowers produce long, dry, pod-like fruits called siliques, which contain the seeds.
The Dramatic Diversity of Brassica oleracea
The species Brassica oleracea is responsible for the most dramatic visual transformations, as selective breeding has maximized different plant parts. All cultivars, from kale to cauliflower, are genetically the same species but have been developed to look drastically different. This single species contains groups developed for their leaves, buds, stems, or immature flower clusters.
Leaf and Bud Forms
Cultivars grown for their leaves, such as kale and collard greens (the Acephala group), feature loose, prominent leaves. These leaves can be smooth, crinkled, or frilly, often forming a robust rosette but never a tight, dense structure. In contrast, plants developed for their dense buds, like head cabbage and Brussels sprouts, exhibit a tightly overlapping leaf structure. The cabbage head is a large, compressed terminal bud, while Brussels sprouts are small, dense lateral buds that form along the main stalk.
Stem and Flower Forms
Other forms emphasize specialized structures, such as the swollen stem of kohlrabi, which develops into a bulbous shape above the soil line. Broccoli and cauliflower represent the maximization of the inflorescence, or flower cluster. Broccoli (Italica group) features a head composed of numerous distinct, immature flower buds. Cauliflower (Botrytis group) forms a dense, compacted mass of undeveloped flower tissue known as a curd.
Distinguishing Features of Other Major Brassica Species
Other major Brassica species look fundamentally different from B. oleracea cultivars, focusing on the development of roots or distinct leaf forms. Brassica rapa includes plants like turnips and bok choy, illustrating a separate visual divergence. Turnips are recognizable by their swollen, fleshy taproot, which is the primary edible part, often accompanied by a hairy leaf rosette. Bok choy, a variety of B. rapa, has a distinct, non-heading structure of thick, white or light green leaf stalks and dark green leaf blades. Brassica juncea, commonly known as mustard greens, is grown for its leaves and has a visually distinct appearance from the smoother-leaved B. oleracea cultivars. The leaves of mustard greens are typically more jagged, serrated, or deeply lobed.