I STUDY the dogs of the plant world. That is the answer you will get if you ask what he does for a living. He will tell you that dogs, despite their dazzling diversity, are all members of a single species – and that the plant species he studies has its own equivalents of pugs, Labradors and Great Danes. He will then recount his odyssey to find this plant’s closest living wild relative – its equivalent of the wolf – to learn how it came to be tamed. It is a tale of Greek gods, island giants and ancient antidotes to intoxication.
Having heard it, you will never see Brussels sprouts in quite the same way. Often overcooked and under-loved, you wouldn’t expect this Christmas stalwart to have an exotic backstory. But the other dishes in your festive spread reveal why it is so fascinating. Whether you are eating cauliflower, Savoy cabbage, broccoli, kale, collard greens or even kohlrabi, all these vegetables belong to a single species: Brassica oleracea.
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Just how you can get such variety from one plant has intrigued scientists, including Charles Darwin, for centuries. It makes B. oleracea a fantastic way to study the power of selective breeding. “Domestication in general is fascinating because it’s like fast evolution,” says Pires, an evolutionary botanist at the University of Missouri. And solving this conundrum could help create new crops that are resistant to climate change.
B. oleracea is the species name of at least 16 different vegetables that come in an incredible range of forms, from the bite-sized Brussels sprout to the giant Jersey cabbage, native to the Channel Islands, which grows into a sort of tree that can be up to 4 metres tall. They were all created by humans over millennia. “Our story is entangled with this one species of plant,” says at the University of Florida. Yet efforts to pin down the identity of its ancestor have proved frustrating.
Weedy, cabbage-like plants are found growing wild along the Atlantic coastline of Europe, and one idea is that B. oleracea was formed by the domestication of these in England. Another hypothesis has it that the Mediterranean, with its vast diversity of cabbages and kales, is the species’ birthplace. Adding to the mystery is the fact that the family tree of B. oleracea vegetables and their relatives is more like a tangled, bushy shrub. That has left researchers struggling to decide how many domestication events the plant has undergone and how many ancestors it had.
To try to settle the matter, Mabry, Pires and their colleagues . First, they turned to the B. oleracea genome, and compared the DNA of 14 of these vegetables and nine wild cabbages. By looking for similarities at specific points in the genomes, they grouped the plants together to understand their evolutionary relationships. This pointed to a weedy-looking plant called Brassica cretica being B. oleracea‘s closest living wild relative. This suggests it could be the wild ancestor of B. oleracea, or very closely related to it, with domestication first occurring around 4200 years ago. B. cretica suns itself on the shores of the Aegean Sea, lending weight to the Mediterranean hypothesis.
The Aegean location is consistent with a by at Bioversity International in Rome, Italy, and his colleagues. The earliest mentions of B. oleracea vegetables are in Greek literature dating from around 2500 years ago. These include advice from the botanist Theophrastus to use the plant to ameliorate the intoxicating effects of alcohol – a myth that persists in parts of southern Italy, says Maggioni. Later, Roman writers describe an explosion of different kinds of B. oleracea, including large-headed cabbages, which weren’t to everyone’s taste. “Pliny even says he was dismayed by seeing these ‘monstrosities’ coming to the market – as if they were the [genetically modified organisms] of the time,” says Maggioni. Such testimonies of the use and diversity of B. oleracea don’t appear in ancient texts from other areas, he adds.
Mabry and Pires’s independent study of cultural sources . What’s more, the habitat in the eastern Mediterranean would have suited B. cretica, according to a reconstruction of its Late Holocene ecology by . It did indeed look as though B. cretica could be the ancestor, and that the Eastern Mediterranean was where humans began to domesticate it – very apt given the Greek legend that cabbages sprung up where Zeus’s sweat fell to the ground.
Feral cabbages
These results are , published this year. The team, led by at Wageningen University in the Netherlands, found that domestication occurred around 4600 years ago in the Middle East. “It’s very close,” says Bonnema. However, the researchers didn’t confirm B. cretica as an ancestor, partly because they didn’t set out to identify one.
So there are still a few loose ends to tie up. Mabry and Pires were unable to sample Atlantic wild-growing cabbages in their genetic analysis. They think these are likely to be feral plants, ones that were cultivated but now grow wild, but they don’t know for sure. “Until there is a confirmation that all the Atlantic plants are not wild, then there is a margin of uncertainty,” says Maggioni. What’s more, there are signs that some of the B. cretica plants Mabry and Pires tested are feral, not wild, hinting that B. cretica itself was domesticated at one point.
This complicates the picture, but it also strengthens the possibility that feral plants played a pivotal role in B. oleracea’s domestication – perhaps lurking on the fringes of cultivated fields and adding their genes into the mix. Feral plants could be crucial to the species’ future, too. Let off the leash, cultivated varieties adapt to local conditions, forming a pool of variation that scientists could draw on to produce vegetables that are better suited to a warmer world. If a feral plant is resistant to herbivores or drought, those genes could be added back in using gene editing, or the plant itself could be re-domesticated.
The next step for Pires and Mabry is to visit, collect and conserve as many wild-growing B. oleracea as possible, including Atlantic wild-growing cabbages. Meanwhile, the sprouts on your Christmas platter continue to evolve as our tastes change. Modern strains have been bred to replace the bitterness with a sweet, buttery flavour. So if you are an inveterate sprout-hater, give them another try. Just don’t boil them to a mush first.
