Extinction rates are expected to increase during the Anthropocene. Current extinction rates of plants and many animals remain unknown. This study represents the first effort to quantify extinctions among the vascular flora of North America north of Mexico since European settlement. We compiled data on apparently extinct species by querying plant conservation databases, searching literature, and vetting the resulting list with botanical experts. Because taxonomic opinion varies widely, we developed an Index of Taxonomic Uncertainty (ITU). The ITU ranges from A to F, with A indicating unanimous taxonomic recognition and F indicating taxonomic recognition by only a single author. The ITU allowed us to rigorously evaluate extinction rates. Our data suggest 65 taxa (51 species and 14 infraspecific taxa) representing 33 families and 49 genera of vascular plants have become extinct in our study area since European settlement. Seven of these taxa exist in cultivation but are extinct in the wild. We found most extinctions in western North America, but that disparity may reflect the timing of botanical exploration relative to settlement. Sixty‐four percent of extinct plants were single‐site endemics, and many occurred outside recognized biodiversity hotspots. Given the paucity of plant surveys in many areas of North America, particularly prior to European settlement, the actual extinction rate of vascular plants is undoubtedly much higher than indicated here. Article Impact Statement: The number of presumed extinct plants from the continental United States and Canada is much greater than previously recognized. This article is protected by copyright. All rights reserved

First posted May 20, 2021 Director, Lower Mississippi-Gulf Water Science Center U.S. Geological Survey 640 Grassmere Park Drive Nashville, TN 37211 The unglaciated southeastern United States is a biodiversity hotspot, with a disproportionate amount of this biodiversity concentrated in grasslands. Like most hotspots, the Southeast is also threatened by human activities, with the total reduction of southeastern grasslands estimated as 90 percent (upwards to 100 percent for some types) and with many threats escalating today. This report summarizes the results of a multistakeholder workshop organized by the Southeastern Grasslands Initiative and the U.S. Geological Survey, held in January 2020 to provide a scientific needs assessment to help inform the Species Status Assessment (SSA) process under the U.S. Endangered Species Act, with a focus on grassland species and communities of conservation concern in the southeastern United States. This report reviews the ecology of southeastern grasslands, including influences on their origin, maintenance, and high species richness and endemism; presents findings from the workshop; and discusses science questions, hypotheses, and possibilities for future research projects to help fill key knowledge gaps. Participants in the January 2020 workshop, representing diverse expertise in various topics in southeastern grassland ecology, were tasked with identifying major threats to grassland species in the Southeast as well as potential ways to make the SSA process more efficient and effective. An underlying assumption and starting place for workshop discussion was that an ecosystem-based approach to the SSA process is more cost-efficient than a species-by-species approach, in large part because many species with similar biological requirements can be addressed by the same actions. Nevertheless, one partner in this effort, the U.S. Fish and Wildlife Service, does require specific attention be given to taxa that have been petitioned for Federal listing, though as often as possible these taxa are considered alongside a larger group of priority taxa with an ecosystem approach. For group discussions, workshop participants followed a modified “World Café” method, a structured conversational approach for knowledge sharing. Group discussions focused on five categories of threats to grassland communities and species: (1) habitat loss, fragmentation, and disruption of functional population connectivity; (2) climate change, especially changes in temperature and precipitation, including intensity and seasonality, and impacts on soil moisture, groundwater levels, and other ecosystem parameters; (3) changes to disturbance regimes, as influenced by climate and land-use change, extinctions, and human attitudes and behaviors; (4) invasive species (not limited to nonnative species); and (5) localized or subregional impacts such as sea-level rise. In addition to group discussions, workshop participants—as well as other grassland experts who were unable to attend the workshop—completed a preworkshop survey concerning challenges and opportunities for grassland conservation. Findings reported here under each of these topics represent ideas, problems, hypotheses, and questions identified by a diverse community of grassland managers and researchers which may be addressed by future research and monitoring in southeastern grassland ecosystems to help guide science-based conservation of grassland-dependent species.

Despite its successes, the U.S. Endangered Species Act (ESA) has proven challenging to implement due to funding limitations, workload backlog, and other problems. As threats to species survival intensify and as more species come under threat, the need for the ESA and similar conservation laws and policies in other countries to function efficiently has grown. Attempts by the U.S. Fish and Wildlife Service (USFWS) to streamline ESA decisions include multispecies recovery plans and habitat conservation plans. We address species status assessment (SSA), a USFWS process to inform ESA decisions from listing to recovery, within the context of multispecies and ecosystem planning. Although existing SSAs have a single‐species focus, ecosystem‐based research can efficiently inform multiple SSAs within a region and provide a foundation for transition to multispecies SSAs in the future. We considered at‐risk grassland species and ecosystems within the southeastern United States, where a disproportionate number of rare and endemic species are associated with grasslands. To initiate our ecosystem‐based approach, we used a combined literature‐based and structured World Café workshop format to identify science needs for SSAs. Discussions concentrated on 5 categories of threats to grassland species and ecosystems, consistent with recommendations to make shared threats a focus of planning under the ESA: (1) habitat loss, fragmentation, and disruption of functional connectivity; (2) climate change; (3) altered disturbance regimes; (4) invasive species; and (5) localized impacts. For each threat, workshop participants identified science and information needs, including database availability, research priorities, and modeling and mapping needs. Grouping species by habitat and shared threats can make the SSA process and other planning processes for conservation of at‐risk species worldwide more efficient and useful. We found a combination of literature review and structured discussion effective for identifying the scientific information and analysis needed to support the development of multiple SSAs. Article impact statement : Species status assessments can be improved by an ecosystem‐based approach that groups imperiled species by shared habitats and threats.

Societal Impact Statement: Understanding the current state of trees within the United States is imperative for protecting those species, their habitats, and the countless communities they support, as well as the ecosystem services they provide. We present an updated checklist of all tree species native to the contiguous United States, their state distribution, extinction risk, and most common threats. Knowledge of national threat “hotspots” and conservation priorities facilitates efficient conservation efforts and the allocation of resources to safeguard the 11–16% of US tree species that are threatened. These results lay the groundwork for tree and ecosystem conservation efforts in the United States that contribute to achieving critical international conservation goals, including the United Nations Decade for Ecosystem Restoration and the Global Tree Assessment.Summary: The Global Tree Assessment aims to complete threat assessments for all the world's ~60,000 tree species, but most species native to the continental United States had either never been assessed or were outdated on the two most widely used threat assessment platforms in the United States, International Union for the Conservation of Nature (IUCN) Red List and NatureServe. There was also no coordinated mechanism for sharing data between these platforms, resulting in missing, duplicated, or outdated information. We (1) created an updated checklist of all tree species native to the contiguous United States based on the standardized Global Tree Assessment tree definition, (2) created over 700 new or updated IUCN Red List assessments and NatureServe Global Ranks, and (3) developed a replicable assessment data sharing process. We present an updated checklist of native US trees that includes 881 species from 269 genera, with Quercus and Crataegus as the most species‐rich tree genera. We present the first country‐wide analysis of tree extinction risk, patterns of geographic and taxonomic diversity, and leading threats. An estimated 11–16% of US tree species are threatened with extinction, with the most common threat being invasive and problematic pests and diseases. We introduce a “crosswalk” process for efficient, large‐scale data sharing between the IUCN Red List and NatureServe, using IUCN Red List Species Information Service (SIS) Connect, which can be applied to other taxonomic groups in North America. The checklist, threat assessments, and crosswalk methodology represent a significant advancement in prioritizing conservation action for at‐risk tree species and restoration of forests in the United States, supporting the global goals of the United Nations Decade for Ecosystem Restoration and the Global Tree Assessment effort.

As part of ongoing efforts to understand, document, and conserve the flora of the southeastern United States, we make new combinations to accord with our generic taxonomy, name a new hybrid, re-recognize a species relegated to synonymy in recent decades, lectotypify and generally clarify nomenclatural issues in several genera, clarify taxonomy and distributions of species, and report important new and current distribution records. In Doellingeria (Asteraceae), we clarify the taxonomy and distribution of D. sericocarpoides and D. umbellata in the region. In Trilisa (Asteraceae), we summarize and clarify the taxonomy, name a new hybrid, and present a new key to the taxa in the genus. Species delimitation in Stillingia (Euphorbiaceae) has been controversial and unsettled in the region, and we examine the confused taxonomy and nomenclature of the genus in the southeastern United States, re-recognizing a species used by J.K. Small, but with an expanded circumscription and a clarification of various nomenclatural issues. We examine typification of Desmodium dillenii (Fabaceae) and its application to our modern understanding of the circumscription of taxa, recommending it be considered a junior synonym of Desmodium glabellum. In Juncus, we assign a lectotype for Juncus anthelatus, fixing its application. In Primulaceae, we discuss the delineation of genera in Lysimachieae, and take a middle path regarding lumping/splitting, supporting the recognition of traditional and monophyletic segregates Trientalis, Steironema, Anagallis, and Centunculus, while treating Lysimachia in a moderately broad sense, including Glaux and multiple subclades; in order to implement this taxonomy in the southeastern United states, we make a single new combination in Steironema. We also discuss generic circumscription in Selaginellaceae, and argue for the recognition at genus rank of six major clades, monophyletic, ancient, and morphologically recognizable; in order to apply this taxonomy in the southeastern United States, we make five new combinations in Bryodesma, Gymnogynum, and Stachygynandrum. Finally, we report important new records of locally, regionally, or globally rare species in North Carolina: Helanthium tenellum, Chenopodium berlandieri var. macrocalycium, Carex barrattii, Carex vestita, Eleocharis compressa var. compressa, Rhynchospora compressa, Rhynchospora sulcata, and Croton michauxii.

This checklist provides the first complete, vouchered account of Maryland’s vascular flora. In total, we discuss 3,525 taxa and document 2,918 established taxa for the state of Maryland, 71.8% of which are native and 28.2% of which are introduced. Of the native species, 737 (25.3%) are tracked by the Maryland Natural Heritage Program as of conservation concern. We exclude 324 taxa reported from Maryland by previous authors and provide justifications for these exclusions.