Microsporogenesis, Megasporogenesis, and Gametophyte Development in the Threatened Tree Buchanania lanzan (Anacardiaceae)

Buchanania lanzan (Spreng.) is a valuable tree species of the Anacardiaceae family, native to the dry deciduous and mixed forests of India, with notable occurrence in the Western Ghats, a recognized biodiversity hotspot. Despite its ecological and commercial importance, detailed knowledge of its reproductive biology has been limited. In this study, we investigated the sequential events of microsporogenesis, megasporogenesis, and gametophyte development through detailed histological observations using light microscopy, fluorescence microscopy, and scanning electron microscopy (SEM), providing new and accurate information on reproductive development. Anther development is tetrasporangiate, with microsporogenesis following the simultaneous type of cytokinesis. Microspore mother cells underwent regular meiosis to produce predominantly tetrahedral tetrads, which developed into bicellular pollen grains at anthesis. Fluorescence staining confirmed high pollen viability, while SEM revealed well-developed exine sculpturing. Structural adaptations such as cuticular outgrowths, trichomes, tannin accumulation, and calcium oxalate deposits highlighted multifunctional roles of the anther wall in protection and pollinator interactions. Ovule ontogeny is anatropous, bitegmic, and crassinucellate. Megasporogenesis results in a linear tetrad, of which only the chalazal megaspore remains functional, giving rise to the Polygonum-type mature female gametophyte. The outer integument exhibited a unique growth pattern that may safeguard the developing embryo sac. The temporal sequence of gametophyte maturation indicated a tendency toward protogyny, which could influence pollination dynamics. These findings resolve previous uncertainties in the reproductive biology of B. lanzan and provide novel insights into sporogenesis, gametophyte development, and associated structural adaptations. The study contributes essential baseline data for conservation strategies, sustainable utilization, and management of this threatened species facing pressures of habitat loss and overexploitation.