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The Romanesco cauliflower, one of the strangest looking vegetables because of its fractal florets, owes its unique shape to the fact that it forms from failed flowers.

Like regular cauliflowers, Romanescos are a product of selective breeding of the plant Brassica oleracea, from which several other common vegetables like cabbage, broccoli and kale also originate.

at the French National Centre for Scientific Research and his colleagues have figured out that cauliflowers, including Romanesco, gain their shape because they start off as flower buds that fail to become flowers. These buds become shoots that make new flowers which also fail – and the process is repeated again and again in a sort of chain reaction.

“Really, what I was thinking immediately was, ‘yay, finally an answer’. These are regular patterns that we see over and over again,” says at the University of Georgia in the US, who wasn’t involved in this research. “We can measure them, but why they are there and how they are controlled biologically was always kind of a bigger question.”

While we still don’t have all the answers, we do now know the biological mechanism through which the fractals form. Parcy and his colleagues studied the genes involved and built a 3D computational model of plant development to explain how this happens.

“They start as flowers then lose their identity,” says Parcy. “If you imagine a firework, it explodes and makes light. It’s like if each of them was exploding again and again. And what you get, the structure of this cauliflower, is the result of all those consecutive explosions.”

The difference between regular cauliflowers and Romanesco is that each individual failed flower is visible in the final Romanesco. This is because Romanesco shoots produce more buds at an accelerating rate which lifts the growing tip away from the centre of the growing cauliflower, creating the familiar array of conical shapes that characterise the Romanesco. Other cauliflower buds are produced at a constant rate, which gives the finished vegetable a different appearance with rounded, hummocky florets.

“The Romanesco is something really, really special. I don’t know any plant that looks like this,” says Parcy. “In a way, it’s written in the code of the plant to make that.”