Mineral and organic inclusions in wood and bark of mangroves from the Indian Sundarbans: their linking with taxonomy and phylogeny

Abstract

Mangroves are specialized intertidal plants that rely on mineral and organic inclusions viz., calcium oxalate crystals (CaOx), tannin, latex, gum and starch grains. These inclusions contribute to structural support (e.g., CaOx crystals), herbivore defense (e.g., CaOx crystals, tannin, and latex), wound sealing and desiccation protection (e.g., gum), physiological resilience under high salinity and tidal stress (e.g., starch grains as osmotic regulators). CaOx crystals may not only hold functional and ecological relevance such as internal Ca homeostasis, Ca recycling, oxalate detoxification and internal carbon reservoirs but also reflect taxonomic and phylogenetic implications. However, a comprehensive anatomical characterization of such inclusions in mangroves’ wood and bark remains underexplored, particularly in relation to their systematic and phylogenetic implications. This study is the first to comprehensively document and compare CaOx crystal morphology, frequency, cellular location, dimensions and elemental composition, along with the distribution of organic inclusions (tannin, latex, gum, starch grains) within mature wood and bark of twenty mangrove taxa from the Indian Sundarbans. We correlated observed crystal morphotypes with molecular phylogenetic framework based on rRNA gene sequences of studied mangrove taxa that reveals strong genus-level consistency and taxonomic cohesion. Distinct crystal morphologies with consistent tissue-specific deposition patterns across genera, serving as supplementary markers for genus-level identification in mangrove systematics. Principal Component Analysis of relative crystal morphotype frequencies supported genus-level clustering of species, indicating taxonomic cohesion of taxa having similar crystal profiles, which is consistent with high intragenic rRNA gene sequence similarity indices, suggesting phylogenetic conservation in crystal traits within each genus. These findings link anatomical data (calcium oxalate crystal traits) and molecular phylogeny of mangroves, offering new insights into mangrove taxonomy, phylogeny and adaptive biology.