Mathematics of phyllotaxis
A rotation by GoldenRatio (1 + √5)/2 turns is equivalent to a rotation by 2 - GoldenRatio GoldenRatio-2 ≃ 0.38 turns, or 137.5°. Successive approximations to this number are given by Fibonacci[n - 2]/Fibonacci[n], so that elements numbered Fibonacci[n] (i.e. 1, 2, 3, 5, 8, 13, ...) will be the ones that come closest to being a whole number of turns apart, and thus to being lined up on the stem. As mentioned on page 891, having GoldenRatio turns between elements makes them in a sense as evenly distributed as possible, given that they are added sequentially.