Impacts of taxonomic change on the Amazonian palm flora

Although species taxonomy is an ever-evolving discipline, taxonomic change is rarely accounted for in macroecological studies. By tracking the history of species description and synonymizations of more than 900 described names of Amazonian palms, we reveal shifts in species counts across space and time, the factors associated with taxonomic lumping, and the time needed to detect synonyms. The Amazonian palm flora results from a gradual accumulation of new descriptions, followed by decline due to the recognition of approximately 800 heterotypic synonyms. Most of these synonyms were detected in the mid-1990s, leading to a 4.5-fold decrease in species counts in ten years. The time to detect synonyms ranged from 3 to 227 years. Species with large populations, widespread distributions, early descriptions, also those that occur in Western Amazonia were more frequently lumped. The impact of taxonomic change on species counts is dependent on taxa, region, and time period considered. Biases in these counts are pronounced in the absence of taxonomic revisions, as undetected synonyms can inflate estimates of species richness. By quantifying the magnitude of such bias, this study offers conceptual and methodological insights on how incorporating taxonomic progress into macroecological analyses can provide a more accurate understanding of biodiversity patterns.