A method for making Red List assessments with herbarium data and distribution models for species-rich plant taxa: Lessons from the Neotropical genus Guatteria (Annonaceae)

Societal Impact Statement: Despite its importance, biodiversity is declining rapidly. To adequately prioritise conservation efforts, we need to know how threatened species actually are. The International Union for the Conservation of Nature (IUCN) Red List is the most widely recognised tool for assessing extinction risk. Unfortunately, many lesser-known species are not yet represented, such as those that are rarely collected or are in species-rich taxon groups. This is potentially due to low data availability, although Red List assessments can still be made with little data. We present a method to rapidly assess the conservation status of species that have low data availability, which will speed up the inclusion of species from large groups into the IUCN Red List. Summary: • The International Union for the Conservation of Nature (IUCN) Red List is the most widely recognised tool to assess the extinction risk of species. For it to be effective in directing conservation effort, it is important that as many species as possible are represented, but many are unfortunately not. A lack of data is often the main reason for this, especially for lesser-studied species. However, this does not mean assessments cannot be made. • We examine the use of georeferenced herbarium data in combination with species distribution modelling for assessing plants on the IUCN Red List, with Guatteria (Annonaceae), a genus of Neotropical trees, as a case study. We focus on differences between preliminary and officially published assessments, show the final conservation status of all Guatteria species and provide a roadmap for compiling Red List assessments for species-rich plant groups in the future. • We found that species-distribution models aid in compiling Red List assessments, especially for taxa that lack data, but expert opinion remains an important source of information. Half of Guatteria species (48.0%) are Least Concern, and 13.1% of species are near threatened or threatened. The remaining species are Data Deficient or Not Evaluated. Most of our preliminary assessments remained unchanged upon review and publication on the IUCN Red List. • Our method allows for assessing a large group of taxa in a relatively short amount of time. We argue that this benefit outweighs the potential disadvantage of a lack of detail in these assessments, emphasising the potential of this method for future Red List assessments.