Karyomorphology of Tithonia diversifolia,an invasive plant in southwest China and its implications in the current distributions

【摘要】：正Ten Tithonia diversifolia populations ranged from tropical to north subtropical climatic conditions,at altitudes of 76-2000 m in Yunnan of SW China,were sampled for the cytological studies. The results showed that chromosome numbers in all the 10 populations were 2n= 34 at metaphase, except some chimera cell type 2n = 32 or 68(less than 5%) in one population,and the basic chromosome number was x = 17.The karyotype variation at the diploid level of all the sampled populations presented some distinguishable cytological characters.Field observations indicated that T. diversifolia presented a great capacity to grow clonally,and the clonal growth and branching process was especially common when adventitious roots and young shoots rapidly emerged from nodes on lower or the prostrate branches,which increased the density of the species community.T.diversifolia has been obviously spread via the road network,which is dominating the geographical distribution in Yunnan of SW China.Based on the comprehensive comparison of karyotype variation,clonal proliferation characters,and the road networks spreading of T.diversifolia,it could be concluded that the wide adaptability of T.diversifolia might relate to its introduction sources,reproductive characters and genetic bases presented at variable chromosome characters.