Robberecht R., Nobel P. S., A Fibonacci Sequence in Rib Number for a Barrel Cactus, Annals of Botany, 1983, 51(1):153-155, doi: 10.1093/oxfordjournals.aob.a086440
The paper describes rib number and addition in Ferocactus acanthodes in Deep Canyon, California. In a sample of 100 randomly selected plants, rib number was compared with stem height and the distribution of ribs between the base and apex. The authors identified frequent Fibonacci sequence values and transitional phases. The link between this pattern, stem development and hydration changes was presented as a functional interpretation.