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Sclerocactus dawsoniae McGlaughlin & Naibauer (Cactaceae), a new species from western Colorado, is described. Sclerocactus dawsoniae is segregated from S. glaucus (K. Schum.) L. D. Benson, differing by having a smaller overall size, fewer spines per areole, an allopatric distribution, and substantial genetic differentiation. 

IntroductionRecent advances in genetic data collection utilizing next-generation DNA sequencing technologies have the potential to greatly aid the taxonomic assessment of species of conservation concern, particularly species that have been difficult to describe using morphology alone. Accurate taxonomic descriptions aided by genetic data are essential to directing limited conservation resources to species most in need.Sclerocactus glaucusis a plant endemic to Western Colorado that is currently listed as Threatened under the Endangered Species Act (ESA). However, in 2023, the U. S. Fish and Wildlife Service proposed de-listingS. glaucusfrom the ESA due to recovery of the species. Previous research had found substantial genetic structure between populations in the northern part of theS. glaucusrange relative to the majority of the species distribution. MethodsIn this study we utilized double-digest Restriction-site Associated DNA sequencing (RAD-seq) in order to better understand the genetic structure ofS. glaucus. ResultsOur results indicate thatS. glaucuscontains two distinct evolutionary lineages that warrant recognition at the level of species, with what was previously described asS. glaucusNorth being recognized asSclerocactus dawsoniae. DiscussionThe newly describedS. dawsoniaehas a limited estimated number of individuals, low levels of nucleotide diversity, a very narrow geographic range, and an uneven geographic distribution with most plants being found in a single management area, all of which supports continued direct conservation of this species. In contrast,S. glaucushas a large estimated minimum population size, a broad geographic range that includes numerous protected areas, and adequate levels of genetic diversity. Without further conservation action, a delisting decision forS. glaucuswill simultaneously remove all Endangered Species Act protections forS. dawsoniae. The current work demonstrates the importance of having robust genetic datasets when planning conservation activities for species of concern. Moving forward, we recommend that government stakeholders prioritize supporting genetic studies of endangered species prior to making any changes to listing decisions. 

Dithiolene-based N-heterocyclic silane demonstrates unusual dual nucleophilic reactivity toward boron halides.