A team of mathematicians and plant scientists have figured out how cauliflowers grow into their peculiar shape.

Experts from the University of Nottingham worked with an international team led by CNRS1 and Inria on the study that revealed that cauliflowers, and Romanescos in particular, are in fact buds that are designed to become flowers but which never reach their goal. The findings have been published in the journal Science.

The research combines mathematical modelling and plant biology to show that instead of reaching flowering stage cauliflowers develop into stems, which in turn continue trying to produce flowers. The cauliflower is born from this chain reaction, resulting in a succession of stems upon stems.

The study shows that the brief incursion of buds into a flowering state profoundly affects their functioning and allows them, unlike normal stems, to grow without leaves and to multiply almost infinitely. The atypical shape of the Romanesco is explained by the fact that its stems produce buds more and more rapidly, whereas the production rate is constant in other cauliflowers.

This acceleration gives each floret a pyramidal appearance, making the fractal aspect of the structure clear. The study highlights how the selection of mutations in plants during the process of domestication has changed their shape, sometimes drastically, into the fruits and vegetables on our shelves.

Assistant professor Etienne Farcot from the University of Nottingham is one of the mathematicians who initiated this research project. He explained: “After over a decade of collaborative work from a multidisciplinary and international team of researchers, this emergent process can finally be explained. Although most plants present a geometric organisation in spirals along main and secondary axes (called 'phyllotaxis'), cauliflowers present an unusual phyllotaxis with a multitude of spirals, nested over a wide range of scales. How such a fractal self-similar organisation emerges from developmental mechanisms has, until now, remained elusive.

'Combining experimental analyses in Arabidopsis thaliana cauliflower-like mutant with mathematical modelling, we found that curd self-similarity arises because growing plant tissues fail to form flowers but keep the 'memory' of their transient passage in a floral state. Understanding this genetic mutation could help plant scientists optimise growth of related plants.”