Differences in characteristics between naturalized threatened plants and other threatened plants

Many non-native plant species introduced by humans have become naturalized. At the same time many species are threatened in their native range. However, the number of plant species threatened in their native range that are naturalized elsewhere remains unknown. So too does the set of characteristics that distinguishes such species from other threatened species. For vascular plant species, we combined information from databases on threat status and naturalization success and information on growth forms, economic uses, and native and non-native ranges to identify plants that are threatened in their native range but naturalized in their non-native range. Among the 26,036 species assessed as threatened by the International Union for Conservation of Nature, only 238 (∼1%) were naturalized elsewhere. Most of the species threatened in their native range that are naturalized elsewhere were trees or shrubs of economic value, for example, for building materials and landscaping. More threatened species than expected were naturalized in Europe, and these include species from nearly all continents. Although Africa was the largest source of species threatened in their native range but naturalized elsewhere in absolute numbers, the numbers were lower than expected due to the continent's overall large number of threatened species. Only a few threatened plant species have become naturalized, and they differed in some of their characteristics, including growth form, native origin, threats, and economic use, from other threatened species.