Extraordinary accuracy in floret position of Helianthus annuus

Abstract

Divergence angles were measured for inflorescences of <em>Helianthus annuus</em> with several hundreds to more than a thousand disk flowers. Quantitative analysis showed that the angles are robustly fixed in the vicinity of the ideal golden angle 137.508° as accurately as ~0.001°. The mean deviation from the ideal value varies for each sample. The results have important implications for phyllotaxis models, which are discussed by referring to a necessary modification proposed by Roberts.