Brassicaceae — the cabbage family
The cabbage family. It is the clearest case in the corpus of one species carrying many crops — cabbage, broccoli, cauliflower, kale, kohlrabi and Brussels sprouts are all Brassica oleracea — and of a family unified by a single class of compounds.
A botanical family. Membership is a fact about the plants and is derived from the verified identities, never listed by hand.
Glucosinolates and the mustard reaction
The family produces glucosinolates, which are inert until the tissue is damaged and an enzyme brings them together with their substrate. The pungency of mustard, horseradish, wasabi and rocket is that reaction, not a stored flavour — which is why these crops taste of nothing until cut, and why processing method changes the product more than cultivar does.
One species, many vegetables
Brassica oleracea has been selected in different directions — terminal bud, flower head, stem, leaf, axillary buds — and each result is a cultivar group rather than a species. That is why they interbreed, why they share pests and diseases completely, and why rotating between them achieves nothing.
Clubroot is the family’s rotational constraint
Clubroot persists in soil for many years as resting spores and infects across the family, so a field with a history of it constrains what can be grown for a long time. Raising soil pH suppresses it and does not eliminate it, and resistance is available but has been overcome by particular pathotypes — so the practical control is a long rotation out of the family.
Biofumigation
The same glucosinolate chemistry is used deliberately: brassica cover crops are incorporated green so that the released isothiocyanates suppress soil organisms. The effect depends on macerating the tissue and incorporating it immediately, which is why biofumigation is a technique rather than simply a crop choice.
Small seed, fast establishment, early bolting
The family’s seeds are small and germinate quickly, and many members bolt in response to cold followed by lengthening days. Vernalisation is therefore a risk in spring-sown crops and a requirement in biennial seed production, and it is the same mechanism in both cases.
What this is not
- Brassica napus appears as both oilseed rape and swede, and Brassica rapa as turnip, pak choi, Chinese cabbage and turnip rape — the family requires the cultivar-group model rather than the species one.
- The vegetables and oilseeds groups both draw heavily on this family, which is why neither grouping predicts what a brassica crop needs.