Yikes! :-)

"Each spiral lattices can be seen as a discrete subgroup of the complex multiplicative group, with the generator Geid. Indeed, in complex notation, points of the lattice can be written as Gkeikd. These form a group isomorphic to the integers (the isomorphism is k-> Gkeikd). Parastichies correspond to cosets of the subgroups 8Z and 13Z in the example given here."

- Brian