Tilia is morphologically well characterized by its unique inflorescence bracts．It is the sole genus of the Tiliaceae in  the  north  temperate，  occurring discontinuously  in  East Asia，Europe-West Siberia and North America，with no common species between these regions．  A taxonomical review is made and 25 species are recognized，of which 17 species are in East Asia，six in Europe-West Siberia and two in North America．The northernmost occurrence of Tilia is represented by T．  cordata in north Scandinavia Peninsula at 66．5°N， and the southernmost by T．mexicana at 17°N in south Mexico．In Europe and East Asia all the species occurring at the northernmost limit belong to Sect．  Tilia，and those at the southernmost are members of Sect．  Lindnera．  An infrageneric system of three sections，  i．e．, Sect．  Trichophilyra，Sect．  Lindnera and Sect Tilia，is followed．  A morphological analysis

reveals that Sect．  Trichophilyra is the most primitive，and Sect． Tilia is the most advanced，and this presumption is also strongly supported by fossil records．  According to Takhtajan’s regionalization of world flora，East Asia is the richest in both species and sections with 17 species in all the three sections，followed by the Circumboreal region with four species in Sect．Lindnera and two in Sect．Tilia．  Accordingly the East Asia region is considered to be the centre of geographical distribution．The fossil distribution is also reviewed．The authentic megafossils of Tilia have been found since Eocene onwards．  The earliest megafossils of Tilia are similar to the existing species of Sect．  Trichophilyra and are found from Spitzbergen，west North America and East Asia．The distribution pattern of fossils is similar to that of existing species．  Based on phylogenetic analysis and fossil findings，the genus Tilia is considered to have originated in subtropical mountains in East Asia in late Cretaceous，and had extended to north Europe and west North America before Eocene．The temperature decline