Plastochron — where it appears
A stem is a cylinder
The sunflower is the photograph, and it is the hard case. Nearly all real phyllotaxis happens on a stem, where the geometry is a lattice on a cylinder with two parameters — and where the spiral counts, which on a disc change with radius, are the same the whole way up.
A growing organ is part of the rule
Every model on this site places primordia on a surface and then treats the surface as furniture. But the surface grows between one placement and the next, and that growth reaches the rule through the only channel it has — where the neighbours are. What looks like a boundary condition turns out to be a term in the model.
Named alongside it
The objects these essays reach for when they reach for this one.
AuxinBasinCylinderCylindrical latticeDescription versus mechanismDivergence angleElongationEpitheliumHonest limitsLadderLocal minimumMechanism