Pollen Morphology and Ancestral Reconstruction Provide New Characters and Evolutionary Insights Supporting The Systematics of The Tribes Adelieae, Caperonieae and Ditaxeae in Euphorbiaceae

Pollen morphology is an important taxonomic character in plant systematics. Notable variations in pollen characteristics are observed in Acalyphoideae (Euphorbiaceae), with aperture types and exine ornamentation having significant roles in taxonomic diagnoses. We describe pollen morphology, support the systematics of the groups, and discuss the evolution of pollen structures in the tribes Adelieae, Caperonieae, and Ditaxeae. Pollen grains of the genera within these tribes are generally medium-sized, except in Chiropetalum tricoccum, which alone exhibits small to medium sized grains. Seven pollen types were identified: Caperonia I, Caperonia II, Adelia membranifolia, Adelia ricinella, Chiropetalum, Philyra brasiliensis, and Argythamnia. The pollen data from the analyzed tribes have important implications for systematics, as Adelia ricinella exhibits a distinct pollen type among the species analyzed due to its microechinate exine. Philyra exhibits pollen grains that, although differing in exine structure, resemble some Caperonia species. Chiropetalum pollen differs from the other genera by the presence of an operculum, while Argythamnia pollen is never operculate. Caperonia exhibits the greatest variation in key diagnostic characters, particularly in terms of its number of apertures. This study provides new palynological characters and ancestral reconstructions that contribute to the evolutionary and systematic understanding of the Euphorbiaceae tribes Adelieae, Caperonieae, and Ditaxeae. These results strengthen recent phylogenetic classification and expand knowledge about pollen diversity and evolution in the subfamily Acalyphoideae.