A high proportion of plant species is predicted to be threatened with extinction in the near future. However, the threat status of only a small number has been evaluated compared with key animal groups, rendering the magnitude and nature of the risks plants face unclear. Here we report the results of a global species assessment for the largest plant taxon evaluated to date under the International Union for Conservation of Nature (IUCN) Red List Categories and Criteria, the iconic Cactaceae (cacti). We show that cacti are among the most threatened taxonomic groups assessed to date, with 31% of the 1,478 evaluated species threatened, demonstrating the high anthropogenic pressures on biodiversity in arid lands. The distribution of threatened species and the predominant threatening processes and drivers are different to those described for other taxa. The most significant threat processes comprise land conversion to agriculture and aquaculture, collection as biological resources, and residential and commercial development. The dominant drivers of extinction risk are the unscrupulous collection of live plants and seeds for horticultural trade and private ornamental collections, smallholder livestock ranching and smallholder annual agriculture. Our findings demonstrate that global species assessments are readily achievable for major groups of plants with relatively moderate resources, and highlight different conservation priorities and actions to those derived from species assessments of key animal groups.
In memory of Betty Fitz-Maurice and Eduardo Méndez. We are grateful to the University of Sheffield and the University of Exeter for housing the Global Cactus Assessment (GCA); for the institutional support of IUCN, in particular staff of the Global Species Programme, the IUCN Species Survival Commission and the IUCN SSC Cactus and Succulent Specialist Group and the office of the Chair of IUCN SSC which made available valuable resources, via the Environment Agency of Abu Dhabi, at a critical juncture in the project; to the donors and hosts who made the eight GCA workshops possible as well as the individuals (in parentheses) who helped with the organization and logistics—Mexico's Comisión Nacional de Areas Naturales Protegidas, Comisión Nacional para Conocimiento y Uso de la Biodiversidad (S. Cariaga and A. López) and Instituto Nacional de Ecología, Conservation International, the North of England Zoological Society, Jardín Botánico Regional de Cadereyta (E. Sánchez and M. Magdalena Hernández Martínez), Desert Botanical Garden (C. Butterworth), the Cactus and Succulent Society of America, Jardin Exotique de Monaco (J.-M. Solichon), the Prince Albert II of Monaco Foundation, Conservation International-Brazil, Instituto Chico Mendes, Instituto Argentino de Investigaciones de Zonas Áridas (R. Kiesling and M. Superina), The Mohamed bin Zayed Species Conservation Fund, Instituto de Ecología y Biodiversidad project P05-002 ICM, Universidad de Chile (P. Guerrero), Fairchild Tropical Botanic Garden (J. Maschinski), National Fish and Wildlife Foundation, Laboratorio de Cactología at the Insituto de Biología UNAM (H. Hernández and C. Gómez-Hinostrosa) and Keidanren Nature Conservation Fund; and to G. Charles, P. Hoxey, J. A. Hawkins, C. Yesson and Sukkulenten-Sammlung Zürich who provided point locality data. B.G. was partially funded by Consejo Nacional de Ciencia y Tecnología grant 0000000000118202. We are indebted to the hard work put in by volunteers P. Durán, E. Hounslow, R. Lee, C. Malone, C. F. Rose, K. Watt and S. Willhoit; to L. Bacigalupe and J. Bennie for assistance with analyses; and to M.L. Ávila-Jiménez, J. Bennie, M.G. Gaston, S. Gaston and five anonymous reviewers for comments on the manuscript.