How can broccoli, cabbage, kale, cauliflower, and Brussels sprouts belong to the same species?

Broccoli, cabbage, kale, cauliflower, and Brussels sprouts belong to the same species, Brassica oleracea, because they are all agricultural forms developed from a single wild ancestor through artificial selection.1

While these vegetables appear vastly different, humans have used selective breeding over centuries to isolate and propagate specific traits. By choosing plants with desired characteristics—such as enlarged leaves, stems, or flower buds—breeders created distinct cultivars adapted for human consumption.213

These variations are classified as different varieties of the same species:

• Leaves: Kale and collards (B. oleracea, variety acephala); head cabbage (B. oleracea, variety capitata); and Brussels sprouts (B. oleracea, variety gemmifera).1
• Flowers and stalks: Broccoli (B. oleracea, variety italica) and cauliflower (B. oleracea, variety botrytis).1
• Stem: Kohlrabi (B. oleracea, variety gongylodes).1

Despite their diverse appearances, they remain genetically linked as members of the same species within the Brassicaceae family.41