Morphological characterization of floral ontogeny in Lagerstroemia indica

BACKGROUND: Lagerstroemia indica L. (Lythraceae) constitutes a globally significant ornamental resource, valued for its prolonged anthesis and vivid floral displays. Elucidating the morphological mechanisms of floral organogenesis is a prerequisite for molecular breeding programs aiming to modify floral architecture (e.g., via stamen petaloidy). While foundational ontogenetic studies have been conducted in L. indica, our understanding of its developmental landscape remains incomplete. Specifically, critical gaps regarding the precise 3-dimensional topology of organ initiation and the dynamic morphological shifts during early meristem stages have yet to be fully resolved. To bridge this gap, this study presents a detailed reconstruction of floral ontogeny in L. indica using a combinatorial approach of Scanning Electron Microscopy (SEM) and paraffin histology. RESULTS: We delineate a precise developmental sequence commencing with sepal initiation and enclosure, followed by the synchronous differentiation of the androecium and gynoecium. A defining feature of the Lythraceae-the delayed initiation (retardation) of petal primordia-was confirmed, with petals emerging distinctively later than reproductive organs. Crucially, our observations characterize the proliferation pattern of the inner androecium: unlike the solitary outer stamens, the inner stamen primordia appear to undergo sequential multiplication from a single initial unit in a characteristic 'zigzag' (alternate) pattern. This process results in the formation of fascicled stamen clusters, providing structural evidence consistent with the mechanism of secondary polyandry (dédoublement) in this species. CONCLUSION: These SEM-based findings offer a detailed three-dimensional interpretation of floral differentiation in L. indica. Notably, this approach enabled us to propose a "zigzag proliferation" model characterizing the development of the inner androecium. Together, these results provide a morphological basis for future investigations into the genetic regulation of floral diversity and the phylogeny of Lagerstroemia.