Siliceous phytoliths in species of the Costaceae and Zingiberaceae families of Sri Lanka

Abstract

Phytoliths, due to their distinctive characteristics and durability, are valuable tools for identifying plant taxa, but their broader application is hindered by limited knowledge. This study aimed to identify phytolith forms and their key discriminative features—shape, margin features, surface ornamentation, and size—in 4 species from the family Costaceae and 14 species from the family Zingiberaceae that grow in Sri Lanka, with the goal of exploring their potential use in taxonomic identification. We also investigated the phytolith mass (per unit weight) among plant species or different plant parts. Phytoliths in leaf, pseudo-stem, and petiole samples (n = 3) from these species were extracted using the wet-oxidation protocol. The samples from species that did not respond were subjected to a modified wet-oxidation protocol, but only Zingiber officinale and Z. zerumbet responded to this protocol. A total of ten phytolith forms were identified across eleven species. Phytolith forms in Hellenia speciosa, Curcuma aromatica, C. zedoaria, and Etlingera elatior are distinctive and allow for their taxonomic identification. However, some species exhibited similar phytolith forms, making taxonomic identification based solely on phytoliths impossible. Although Zingiber officinale Type I phytoliths are SPHEROIDAL NODULATE, this species can still be distinguished by its unique Type II phytoliths (PYRAMIDAL NODULATE), which are specific to Z. officinale. In all species, phytolith shapes were consistent across all plant parts (p > 0.05). With the exception of Hellenia speciosa, phytolith size varied significantly depending on the plant part (p < 0.05). Additionally, the mass of phytoliths per unit weight differed significantly between species and among plant parts (p < 0.05), with the highest mass found in leaves. Notably, we identified new phytolith features, contributing to the refinement of phytolith nomenclature. Our findings highlight the potential of phytolith analysis for plant identification and underscore the need for further research to enhance its broader applicability in multidisciplinary studies.