Periodic branched columns are observed for the first time in a layer o
f phase-separate magnetic colloid confined in a cell. The periodicity
lambda scales with the layer thickness L. In the thin limit, where no
branching occurs, lambda is-proportional-to L1/2. In the thick limit,
each column develops a tree structure with branches and roots, and the
columns are separated by shrubs while the scaling relation crosses ov
er to lambda is-proportional-to L2/3.