  Inspired by river networks and other structures formed by Laplacian growth,
we use the Loewner equation to investigate the growth of a network of thin
fingers in a diffusion field. We first review previous contributions to
illustrate how this formalism reduces the network's expansion to three rules,
which respectively govern the velocity, the direction, and the nucleation of
its growing branches. This framework allows us to establish the mathematical
equivalence between three formulations of the direction rule, namely geodesic
growth, growth that maintains local symmetry and growth that maximizes flux
into tips for a given amount of growth. Surprisingly, we find that this growth
rule may result in a network different from the static configuration that
optimizes flux into tips.
