This paper deals with the investigations on the nucleation and growth of Zinc Oxide (ZnO) nanostructures in a catalyst free synthesis. The ZnO nanostructures have been formed by evaporation of Zn (99.99%) in O-2 and Ar atmosphere in single zone furnace under two temperature regions, region A (similar to 1173-1073 K) and region B (similar to 873-773 K). Through application of XRD and TEM techniques, it has been shown that first ZnO is formed which changes to ZnOx through creation of oxygen vacancies. The ZnOx acts as self-catalyst and leads to formation of various nanostructures. Those observed in the present investigation are nanotetrapods (1D, diameter similar to 70-450 nm, length similar to 2-4.5 mu m) nanorods (1D, diameter similar to 45-95 nm, length similar to 2.5-4.5 mu m), nanoflowers(2D, central core diameter similar to 90-185 nm, length of petals/nanorod similar to 1.0-3.5 mu m) and nanoparticles (3D, size similar to 0.85-2.5 mu m). These nanostructures have been revealed by SEM explorations. Attempts have been made to explain the formation of the various nanostructures in terms of the creation and distribution of the ZnOx, the temperature as well as oxygenation conditions.