Curved Reaction-Diffusion Fronts Generate Quasi-Symmetric Phyllotaxis in a Chemical Turing System.

Chemical systems provide controllable platforms for uncovering general principles of self-organization. Phyllotactic structures are a prominent example of natural patterns, arising when radial growth is coupled to spot formation with an intrinsic spatial wavelength. Although Turing reaction-diffusion models can generate phyllotactic patterns, this connection has not been demonstrated experimentally in an established chemical Turing system. Here we show that a propagating front in the chlorine dioxide-iodine-malonic acid reaction converts front-localized spot formation into phyllotactic organization. A planar front produces staggered, locally hexagonal rows, whereas curved fronts organize successive rows into paired, quasi-symmetric parastichy families. The experiments reveal two geometry-dependent subtypes: a radius-scaling form during radial expansion and a wavelength-preserving form during radial contraction. Expansion maintains near-half-wavelength row offsets; contraction produces more variable, frequently smaller offsets. These results establish an experimental link between chemical Turing pattern formation and phyllotaxis.