The Red List of Acer: revised and extended, gives IUCN Red List assessments for all 158 species of Acer. It is an expansion on The Red List of Maples published in 2009. The report finds, 1 in 5 species of Acer are threatened with extinction in the wild. China, is a maple diversity hotspot and many species are threatened here. It identifies the major threat to the genus as urbanisation, as well as other human land use changes.