Fibonacci numbers in phyllotaxis : a simple model
  A simple model is presented which explains the occurrence of high order Fibonacci number parastichies in asteracae flowers by two distinct steps. First low order parastichies result from the fact that a new floret, at its appearance is repelled by two former ones, then, in order to accommodate for the increase of the radius, parastichies numbers have to evolve and can do it only by applying the Fibonacci recurrence formula. 
Gilbert Zalczer
cond-mat.soft q-bio.TO