Broccoli, cabbage, cauliflower, kale, Brussels sprouts, kohlrabi, and collard greens are all the same species: Brassica oleracea. They look nothing alike, but every one of them descends from a single wild plant that ancient farmers selectively bred over thousands of years, each time choosing a different part of the plant to exaggerate. Beyond these closest siblings, broccoli has dozens of more distant cousins in the mustard family, including radishes, arugula, turnips, and horseradish.
The Same Species, Wildly Different Vegetables
Most people know that dog breeds are all one species. Fewer realize the same is true for broccoli, cabbage, cauliflower, kale, Brussels sprouts, and kohlrabi. Charles Darwin himself used these vegetables to illustrate how selection can reshape a single organism into dramatically different forms. Genetic research published in Molecular Biology and Evolution points to a wild Mediterranean plant called Brassica cretica, native to the Aegean region, as the closest living relative of all cultivated B. oleracea crops. As humans carried this plant westward across Europe, they bred it into the variety of modern crop types we eat today.
What makes each vegetable distinct is simply which part of the plant early farmers selected for:
- Broccoli (var. italica): bred for its large, edible flower heads and thick stems.
- Cauliflower (var. botrytis): also bred for its flower head, but one that stays tightly compact and pale.
- Cabbage (var. capitata): bred for tightly packed leaves forming a dense head.
- Kale (var. acephala): bred for large, loose leaves with no head at all.
- Brussels sprouts (var. gemmifera): bred for many small buds along a tall stem.
- Kohlrabi (var. gongylodes): bred for a swollen, bulb-like stem.
- Collard greens: a form of kale selected for broad, flat leaves.
Genetic studies show that many of these cultivar groups don’t form neat, separate branches on a family tree. Broccoli, for instance, is “paraphyletic,” meaning different broccoli varieties are sometimes more closely related to cauliflower or kale than to each other. Kale appears to have been independently selected multiple times from different wild populations. In short, the boundaries between these vegetables are blurrier than the grocery store suggests.
Romanesco, Chinese Broccoli, and Broccolini
Romanesco is the fractal-looking vegetable sometimes labeled “romanesco broccoli” or “Roman cauliflower,” though it’s technically neither. It’s its own cultivar of Brassica oleracea, dating back to 16th-century Italy. Its striking cone-shaped florets spiral outward in a self-similar pattern, each small cone a miniature replica of the whole head. Nutritionally and genetically, it sits somewhere between broccoli and cauliflower.
Chinese broccoli (gai lan or kai lan) is another Brassica oleracea variety, bred in China for its thick stems and small florets. In the 1990s, a Japanese seed company crossed gai lan with conventional broccoli to create broccolini, the long-stemmed, small-headed vegetable now common in supermarkets. Broccolini is a hybrid, but both of its parents belong to the same species.
Lookalikes That Aren’t Siblings
Broccoli rabe (also called rapini) confuses a lot of people because of its name and leafy, floret-topped appearance. It is not a type of broccoli. Broccoli rabe belongs to Brassica rapa, a completely different species that also includes turnips, napa cabbage, and bok choy. It’s a cousin, not a sibling. If you’ve noticed that broccoli rabe tastes more bitter and peppery than broccoli, the species difference is why.
Turnips, despite looking nothing like broccoli, are in that same Brassica rapa group and share a closer genetic relationship with broccoli rabe than broccoli itself does.
The Wider Mustard Family
All of the vegetables above belong to the Brassicaceae family, commonly called the mustard or cruciferous family. This is a huge plant family, and it includes many foods you might not immediately connect to broccoli:
- Radishes (Raphanus sativus)
- Horseradish (Armoracia rusticana)
- Watercress (Nasturtium officinale)
- Arugula (Eruca vesicaria)
- Mustard greens (Brassica juncea)
The sharp, peppery bite common to all these plants is a family trait. It comes from compounds called glucosinolates, sulfur-containing molecules that the plant produces as a defense against insects. When you chew a raw radish or a broccoli floret and taste that distinctive kick, you’re tasting the same class of chemical.
How Nutrition Compares Across the Family
Because broccoli’s closest relatives share the same genetic blueprint, their nutritional profiles overlap significantly. But the differences are worth knowing if you’re trying to maximize specific nutrients. Per 100 grams of raw vegetable, using USDA data:
Vitamin C is nearly identical across the three most popular relatives: broccoli delivers 91 mg, kale 93 mg, and Brussels sprouts 85 mg. Where they diverge is vitamin K. Kale contains 390 micrograms per 100 grams, almost four times broccoli’s 102 micrograms. Brussels sprouts land in between at 177 micrograms. For calcium, kale dominates at 254 mg compared to broccoli’s 46 mg and Brussels sprouts’ 42 mg.
Fiber content also varies. Kale and Brussels sprouts provide roughly 4 grams per 100-gram serving, while broccoli comes in at 2.4 grams. Calorie counts are all low, ranging from 35 (kale) to 43 (Brussels sprouts), with broccoli at 39.
The real nutritional star of the family, though, is a group of compounds that your body converts into sulforaphane, a molecule studied extensively for its antioxidant and anti-inflammatory properties. Broccoli seeds have the highest total glucosinolate concentration of any of the nine Brassica crops measured in one comparative study, at nearly 111 micromoles per gram of dry weight. This is part of why broccoli sprouts have become popular as a concentrated source of these compounds. Cabbage seeds, interestingly, contain more of the specific sulforaphane precursor (glucoraphanin) than broccoli seeds do, but broccoli’s overall glucosinolate profile is richer and more diverse.
Why This Matters in the Kitchen and Garden
Knowing these relationships has practical value. If you’re rotating crops in a garden, all Brassica oleracea varieties share the same pests and diseases. Planting broccoli where you grew cabbage last year invites the same problems. Club root, cabbage worms, and aphids don’t distinguish between siblings.
In the kitchen, the family connection means these vegetables are largely interchangeable in recipes that call for a cruciferous element. Roasted cauliflower can stand in for broccoli. Shaved Brussels sprouts work in place of cabbage in slaws. The flavors differ, but the textures and cooking times are similar enough to swap freely. And because the health-promoting glucosinolates are a shared family trait, eating any mix of these vegetables delivers similar protective benefits. Variety across the family is more useful than loyalty to a single member.