<p>The Ruddlesden–Popper (RP) layered perovskite family is well known for its diverse functionalities. RP members are amenable to structural changes when subjected to a change in temperature. A minor change in the structure of a given RP member substantially influences the resultant functionality of each structural variant. It is therefore essential to decipher such preferred structural variations, planar defects, and their morphology in the as-synthesized sample at ambient conditions, prior to its use for functional applications. Ca₃Mn₂O₇ (<i>n</i> = 2) RP member is synthesized through the Pechini citrate gel technique. X-ray diffraction and transmission electron microscopy techniques have been used to demonstrate the coexistence of orthorhombic A2₁am (SG# 36) and Acaa (SG# 68) structural phases in the as-synthesized sample at ambient conditions. The experimental observation is supported by density functional theory calculations. This confirms that the A2₁am and Acaa orthorhombic Ca₃Mn₂O₇ structural phases are energetically comparable and structurally stable. A 90° oriented merohedral twin variant of the orthorhombic A2₁am phase is experimentally observed along the [001] axis. The nano-lamellae type morphology of these variants is observed with interfaces parallel to the (001) plane. The lamellae are stacked along the [001] direction. The two coexisting phases differ structurally by a variation in octahedral tilting distortion and A-cation displacement.</p> Graphical Abstract <p></p>