The variability of Amazonian palm phytoliths

The Arecaceae (palm) family is one of the most common and economically important plant groups in Amazonia, and play large roles in ecosystem functioning and carbon dynamics. The modern dominance of palms may be a result of environmental gradients, past climate variability and legacies of past human activities. To understand the roles people and environment have played in shaping the abundance and widespread occurrence of Amazonian palm species, past vegetation reconstructions using palaeoecological proxies that can identify palm species or genera are needed. Phytoliths are siliceous microfossils abundantly produced in palms and are used to reconstruct past vegetation composition. The aim of this paper was to assess the variability of Amazonian palm phytolith morphotypes and to determine which morphological characteristics can be used to increase the taxonomic resolution of palm identifications. Phytolith size, sphericity, spinule traits and number of (surficial) projections were measured for 24 Amazonian palm species. Differences were compared using PCA and ANOVA or Tukey tests, followed by Kruskal-Wallis or Dunn tests. Results show potential for phytoliths of Aiphanes aculeata, Attalea maripa, Bactris simplicifrons, Dictyocaryum fuscum, Euterpe precatoria, Iriartea deltoidea, Oenocarpus bacaba, Socratea exorrhiza and the genera Geonoma, Bactris, Euterpe and Oenocarpus to be identified based on their size, shape or number of projections. This will allow future phytolith analyses to reconstruct past palm abundances with an increased taxonomic resolution. We have formulated our findings into a ‘quick guide’ to identify palm phytoliths and test hypotheses regarding the drivers of modern palm distributions and abundances.