This confusion may lead to over- or under-estimation of the real level of invasion or naturalization in a given region, and is also an obstacle for comparative research on the spread of alien plants around the world. For the purpose of this study, the terms used in the present paper are defined here strictly according to concepts suggested by Richardson et al. (2000) and Pyšek et al. (2004). Alien plants in China are all those which have their origins outside China and were introduced intentionally or accidentally. Naturalized plants are alien plants that sustain self-replacing populations for at least 10 years without

direct intervention by people and which are capable of independent growth. Invasive plants are a subset of naturalized plants which produce reproductive offspring, and have spread beyond their area EPZ-6438 nmr of introduction. The term “invasive” used here is defined without any inference to environmental or economic impact. Catalogue of naturalized species We compiled a nationwide list of the current naturalized flora of China (Appendix S1), based on the list of 233 invasive plant species in China released by the Institute of Plant Protection (IPP), Chinese Academy of Agricultural Sciences (CAAS) (2008) (http://​www.​agripests.​cn),

regional lists of invasive and naturalized plant species, and various other publications released before October 2010 (references listed in Appendix S1). Only this website plant species with foreign origins were considered as naturalized, and so a number of species that have been considered by some authors as naturalized in Protein kinase N1 some regions of China but native to other regions of the country were not included. For example, many species native to south China were identified as naturalized and invasive species in Hong Kong or Taiwan; we deleted these in the present list. The synonyms of some species were corrected to their accepted names according to the ‘Catalogue of Life, China, 2009 Annual Checklist’ (http://​data.​sp2000.​cn/​2009_​cnnode_​c/​search.​php),

or the ‘Flora of China’ (1959–2002) (Editorial Board for Flora of China). The naturalized status, origins, life forms of these species were extracted from these references, and were further corrected one by one following the ‘Flora of China’ or various provincial floras. Data analysis We calculated the number and proportions of naturalized species per family and genus in China and the world; we further compared the ratios with equivalent global patterns using linear correlation analysis. We also calculated the proportions of species in each category of origin, life form. Because information on the native distribution of species provided in different references is not always consistent, we grouped species by broad categories, i.e., “Africa”, “America”, “Asia”, “Europe” and “Oceania”.