Pollen as a powerful tool for taxonomic classification in the genus Zingiber (Zingiberaceae)

Palynological studies of Zingiber Mill. (Zingiberaceae) in Peninsular Malaysia remain sparse, limiting their taxonomic and evolutionary interpretation. This study provides the most comprehensive regional assessment, covering 29 species and representing the largest pollen dataset for the genus in this region. Our results demonstrate that pollen morphology, particularly exine sculpturing, unambiguously separated sect. Cryptanthium from sect. Zingiber, whereas pollen size and shape showed substantial overlap. Sect. Cryptanthium is consistently characterized by striate ornamentation, whereas sect. Zingiber exhibits broader diversity, including cerebroid, areolate, micro-rugulate, and verrucate patterns. Contrary to long-standing assumptions, exine morphology shows no consistent correlation with inflorescence orientation, exposing the limitations of peduncle-based sectional delimitation. Palynological evidence further clarified species boundaries, distinguishing morphologically similar taxa (e.g. Z. puberulum vs. Z. aff. puberulum) and supports the distinct status of Z. citrinum from its synonym Z. griffithii. Evolutionary trends suggest striate sculpturing represents the ancestral state, with cerebroid and areolate forms derived; however, this interpretation remains tentative and requires validation through integrated molecular phylogenetic analyses. Overall, this study establishes pollen morphology as a powerful and independent tool for Zingiber systematics, which could be relevant for applied palynological studies.