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.

中文翻译：

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美国和加拿大大陆的维管束植物灭绝


人类世期间灭绝率预计会增加。目前植物和许多动物的灭绝速度仍然未知。这项研究是自欧洲殖民以来首次量化墨西哥北部北美维管植物群灭绝情况的研究。我们通过查询植物保护数据库、搜索文献并与植物学专家审查结果列表，汇编了明显灭绝物种的数据。由于分类学观点差异很大，我们制定了分类学不确定性指数 (ITU)。 ITU的范围从A到F，A表示一致的分类学认可，F表示仅由单一作者的分类学认可。国际电联允许我们严格评估灭绝率。我们的数据表明，自欧洲殖民以来，代表 33 个科和 49 个维管植物属的 65 个类群（51 个物种和 14 个种下类群）在我们的研究区域已经灭绝。其中七个类群存在于栽培中，但在野外已经灭绝。我们发现大多数灭绝发生在北美西部，但这种差异可能反映了植物探索相对于定居的时间安排。百分之六十四的灭绝植物是单一地点特有的，其中许多发生在公认的生物多样性热点地区之外。鉴于北美许多地区缺乏植物调查，特别是在欧洲定居之前，维管束植物的实际灭绝率无疑比此处所示的要高得多。文章影响声明：美国大陆和加拿大推测的灭绝植物数量比之前认识的要多得多。本文受版权保护。版权所有。