Brassica — one genus, many crops
The genus in which a handful of species carry a disproportionate share of the world’s vegetables and one of its major oilseeds. It is published as a hub because the genus itself explains something: which crops can be crossed, which share pests, and why several unrelated-looking vegetables cannot be rotated against each other.
A botanical genus. Published only where several agriculturally distinct crops sit inside one genus and the genus itself explains something about them.
The triangle of U
The cultivated brassicas are related by a documented pattern: three diploid species — Brassica rapa, B. nigra and B. oleracea — and three amphidiploids formed by hybridisation between pairs of them, including B. napus and B. juncea. That relationship is why some crosses are possible and others are not, and why oilseed rape shares a genome with both turnip and cabbage.
Why rotation between brassica vegetables does not work
Because so many of these crops are the same species or share a genome, they share their soil-borne pathogens completely. A rotation of cabbage, then cauliflower, then kale is a continuous brassica crop as far as clubroot is concerned, and the rotation that matters is the one out of the genus.
The same species under different names
Brassica rapa is turnip, pak choi, Chinese cabbage and the turnip-rape oilseed; Brassica oleracea is six familiar vegetables; Brassica napus is oilseed rape and swede. A reader who knows only the common names has no way to see those relationships, and the practical consequences — shared disease, cross-pollination in seed crops, shared cultivar-group modelling — all follow from them.
Seed production and isolation
Most cultivated brassicas are insect-pollinated and largely self-incompatible, so seed crops of different cultivars of the same species will cross freely. Isolation distances in this genus are consequently substantial, and a flowering brassica vegetable near a seed crop is a contamination source rather than a neighbour.
What this is not
- The Brassicaceae family hub covers the chemistry and the family-wide constraints; this hub covers what the genus specifically implies about crossing and rotation.
- Mustard is held in this corpus under a contested generic placement — one authority moves it to a nothogenus — which the identity layer records.