The head of broccoli you steam for dinner and the pungent mustard condiment may seem unrelated due to their dramatically different appearances and uses. However, the answer to whether they are related is a definitive yes. These two plants share a common ancestry that places them together in the same large botanical group, known as a plant family. This close relationship explains why they share certain characteristics, such as a signature flavor profile.
The Family Connection: Brassicaceae
Broccoli (Brassica oleracea group Italica) and various mustard plants, like black mustard (Brassica nigra) or white mustard (Sinapis alba), all belong to the plant family Brassicaceae. This family is commonly referred to as the mustard or cabbage family. Historically, it was also known as Cruciferae, meaning “cross-bearing,” due to the distinctive cross shape formed by the four petals of their flowers.
A primary shared trait is the presence of sulfur-containing compounds called glucosinolates. These compounds are stored in the plant cells and are responsible for the characteristic pungent, sometimes bitter, flavor common to all members of the family. When the plant tissue is damaged, an enzyme called myrosinase converts the glucosinolates into biologically active molecules like isothiocyanates. These compounds are known for their sharp taste and are linked to potential health benefits. The genetic blueprint for creating these specific chemical compounds is a clear indicator of their shared evolutionary history.
Understanding Botanical Classification
The relationship between broccoli and mustard is understood through the Linnaean system of taxonomy, which organizes life into a hierarchy of categories. This system moves from broad categories down to specific ones: Kingdom, Phylum, Class, Order, Family, Genus, and Species. The “Family” designation, in this case Brassicaceae, is a relatively broad level of classification.
The shared Brassicaceae family confirms that broccoli and mustard evolved from a single common ancestor. However, their scientific names show where their paths diverged into distinct plants. Broccoli belongs to the genus Brassica, while white mustard belongs to the separate genus Sinapis. This difference in genus explains the significant visual and biological differences, even though they still share the same family.
Cousins on the Dinner Plate
The Brassicaceae family includes many of the most common and varied vegetables we consume regularly. This family includes not only broccoli and mustard but also a wide array of other culinary staples. Many of these relatives, like broccoli, share the genus Brassica, demonstrating significant genetic flexibility.
Other members of the Brassica genus include:
- Cabbage
- Kale
- Cauliflower
- Brussels sprouts
- Kohlrabi
Outside of the Brassica genus, but still within the Brassicaceae family, are relatives like radish, which belongs to the genus Raphanus. The diversity of these vegetables highlights the ability of a single plant family to be shaped into numerous edible forms.
The Role of Selective Breeding
The striking difference in appearance between a mustard seed and a head of broccoli is largely due to human intervention. The dramatic variations seen among Brassicaceae vegetables are the result of selective breeding, also known as artificial selection. This process involves humans intentionally choosing and breeding plants that exhibit desirable traits, exaggerating those characteristics over thousands of years.
Broccoli, cauliflower, cabbage, kale, and Brussels sprouts are all cultivars of the exact same species, Brassica oleracea. The wild ancestor was a coastal plant that did not resemble any of these modern vegetables. Early farmers selected for plants with large terminal leaf buds, which eventually became cabbage. Others selected for suppressed stem growth and enlarged flower clusters, leading to the development of broccoli and cauliflower. By selecting for different parts of the ancestral plant—such as the leaves for kale or the lateral buds for Brussels sprouts—humans engineered a wide range of distinct vegetables from a single species.