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According to the authors of this latest paper, the spiral phyllotaxis of cauliflower is unusual because those spirals are conspicuously visible at several different size scales, particularly in the Romanesco variety. They maintain that cauliflowers are basically failed flowers. The whole process depends on those branched tips, or meristems, which are made up of undifferentiated cells that divide and develop into other organs arranged in a spiral pattern. In the case of cauliflower, these cells produce buds that would normally bloom into flowers. Those buds develop into stems instead, but unlike normal stems, they are able to grow without leaves and thereby produce even more buds that turn into stems instead of flowers.

This triggers a chain reaction, resulting in that trademark pattern of repeating stems upon stems that ultimately forms the edible white flesh known as the "curd." In the case of the Romanesco variety, its stems produce buds at an accelerating rate (instead of the constant rate typical of other forms of cauliflower). So its florets take on that distinctive pyramid-like shape that showcases the fractal patterns so beautifully.

The puzzle, per the authors, is how these gene regulatory networks that initially evolved to produce flowers were able to change so drastically. So co-author Eugenio Azpeitia and several colleagues combined in vivo experiments with 3D computational modeling of plant development to study the molecular underpinnings of how buds form in cauliflower (both edible cauliflower and the Romanesco variant).

And finally,

"These results reveal how fractal patterns can be generated through growth and developmental networks that alter identities and meristem dynamics," the authors concluded. "Our models now clarify the molecular and morphological changes over time by which meristems gain different identities to form the highly diverse and fascinating array of plant architectures found throughout nature and crops."

Journal Reference:
Eugenio Azpeitia, Gabrielle Tichtinsky, Marie Le Masson, et al. Cauliflower fractal forms arise from perturbations of floral gene networks [$], Science (DOI: 10.1126/science.abg5999)

Original Submission