Flower dimorphism and flower mechanisms in the andromonoecious tree Crateva tapia L. (Capparaceae)

Abstract

The Neotropical Capparaceae include key tree and shrub species that are vital components of arid and semi-arid ecosystems. However, various reproductive traits remain underexplored, limiting our understanding of their pollination mechanisms. This study provides the first anatomical analysis of floral development in the andromonoecious tree Crateva tapia L. We documented inflorescence composition, measured flowers across developmental stages, and statistically compared floral traits between mature perfect and staminate flowers. Reproductive anatomy was analyzed using light and fluorescence microscopy. We established an acropetal sequence of eight stages within a corymbose raceme. Perfect flowers are located at basal nodes and mature first, while staminate and immature perfect flowers are interspersed in upper rachis positions. Sexual dimorphism becomes visually evident at stage 4, coinciding with microspore tetrad formation. In perfect flowers, the gynophore and gynoecium continue to enlarge, containing ovules at the archesporial stage; conversely, female structures arrest development in staminate flowers. At anthesis, staminate flowers exhibit significantly longer anthers and a higher percentage of viable pollen grains than perfect flowers. Perfect flowers show intrafloral protogyny and approach herkogamy, with the stigma positioned above the anthers. This study establishes a baseline for understanding the floral adaptations of C. tapia, pinpointing the precise timing of developmental divergence in Capparaceae flowers, marked by pistil abortion from pre-meiotic stages and differential progression of functional organs.