Large quantities of rhombohedra and elongated rhombohedra boron suboxide platelets with flat (0 0 1) surface have been synthesized through conventional solid state reaction. Detailed structural investigations by selected area electron diffraction (SAED) and high-resolution electron microscopy (HRTEM) of these platelets are presented. We present the direct experimental observation of extensive lateral (0 0 1) microtwins in rhombohedra platelets and they give rise to the fractional diffractions spots. It is believed that the growth of these rhombohedra platelets is prompted by the twin-plane reentrant edge (TPRE) mechanism. The transition from rhombohedra platelets to elongated rhombohedra platelets in morphology is probably the result of catalytic growth at the apexes of the platelets. This proposed growth model can be representative of various platelets with low defects formation energy, especially in twinned crystals having a rhombohedra structure. Besides, the presence of extensive microtwins will yield interesting physical properties and probably results in the broadening of photoluminescence (PL) spectra from the rhombohedra and elongated rhombohedra platelets. (C) 2010 Elsevier B.V. All rights reserved.