The wild cabbage,Brassica oleracea L., on the coasts of western Europe, shows enormous increase in size when taken into cultivation. It shows much variation, which is correlated with its self-sterility. It has the potentiality for producing, since its cultivation began, perhaps early in the Neolithic, kale, brussels sprouts and cabbage. But the historical evidence favours the derivation of cabbage and kale from Italy in pre-Roman times. It would be interesting to compare the wildB. oleracea of Italy (B. Robertiana J. Gay) with the species as found on the coasts of western Europe.
The middle and eastern Mediterranean contains several species nearly related toB. oleracea. Probably cauliflower and broccoli came fromB, cretica, the most eastern of these; and such cultigens as kohlrabi may have been derived from one of the middle Mediterranean species. The various cultivated forms appear therefore to have had a polyphyletic origin.
Enormous increase in size is a feature ofB. oleracea when introduced into cultivation from a chalk soil. The F1 from cabbage x kale is closely similar and is apparently a case of reversion to the ancestral type on crossing two of the derivatives.