Drivers of variation in synonym numbers of angiosperm species names

Abstract Synonyms are an integral part of the taxonomic process, reflecting how its knowledge evolved over time. However, synonyms frequently introduce taxonomic noise into biodiversity databases, making it essential to understand the factors that drive synonym accumulation. While earlier studies have highlighted intrinsic drivers such as nomenclatural practices, taxonomic placement, and the age of accepted names, broader macroecological (e.g. range size) and biogeographical influences remain comparatively understudied. We analysed 347 917 accepted angiosperm names across 421 families and 13 841 genera, covering 355 botanical regions worldwide. Using a multi-predictor generalized linear mixed model framework, we examined the effects of the age of the accepted name, range size, and broad-scale biogeographical distribution patterns on synonym numbers. Each variable contributed positively and consistently to synonym accumulation. The combined model explained 66% of the global variation in synonym number. Our findings show that the age of the accepted name primarily increases the likelihood of independent naming events. Likewise, wide-ranging species are more likely to accumulate synonyms, partly due to the geographical separation among taxonomists. These results offer quantitative insights into taxonomic redundancy at a global scale, which are probably relevant beyond angiosperms and may help prioritize floristic revisions and database curation.