Mobile iodine anions are shown to cluster in large size isotropic fractal patterns (Diffusion Limited Aggregates, DLA) in ion conducting polymeric system PEO:NaI (and also PEO:NH4I). Anisotropic "tree-like" patterns have also been obtained by deliberately creating physical interface such that the aggregating species arrive only from one direction. The aggregating species is I-3(-) which may thermally relax leading to the breaking up of the fractal arms. It is further shown that in the regions where I-2 (instead of I-3(-)) gets formed, a "strain-field" results forbidding further anion clustering.