Phytogeography is interested in the delimitation of  floristic sets and in the origin  of their different elements，while areography focuses its attention on the form and size of geographical range of species and other taxa．  Ecology or，more precisely，ecogeography，answers questions on the reasons for the form and size of areas．  From the current distribution maps of the 247 endemic genera of seed plants of China，it is possible to envisage five main models of partitioning：contiguity (A1-A2)；inclusion(B1-B2)；overlap(C1-C2)；solitary (D1-D2) and disjunction  (E1-E2)．  Many species appear to be limited in at least part of their geographic ranges by physical factors，such as temperature regime，water availability， and geographic and topographic accidents．  For an endemic genus that has not reached a barrier，  its size of area depends upon the capacity of species to adapt to different enviroments

 and to colonize different habitats．  Speranskia with three species，for example，  has a fairly  extensive range in eastern China，but within its area it grows on forested slopes，in thickets， in weedy places，  on roadsides，  near habitations and in steppe area．  The genus Notoseris  with 14 species，however，has a smaller range across south central and southeastern China， but within its area its local distribution is confined strictly to the edges of forests and grassy slopes in forested areas．  Above,examples show that the genera with a high number of species  are not certainly more widespread than the genera with a low number of species．  The conditions of topography that modify the shape of climatic regions (such as altitude，basin，proximity to large bodies of water，etc. ) also modify the shape of major areas，because climatic  boundaries constitute the principal boundaries of floristic and vegetational areas． More local features of topography affect the shape of smaller areas and determine the shape of areas． In  the study of generic areas，it should be clearly emphasized that it is of extreme importance to focus attention on the distributional patterns of species，which may show great significance