Abstract: A karyomorphological study was performed on 3 Alstonia species in Yunnan Province, China . The karyotype of A. rostrata is reported for the first time . The results show that the chromosome numbers in the 3 species are 2n = 42 , and the chromosome numbers of A. scholaris and A. yunnanensis are both unexpectedly different from the previous reports“2n= 44. The interphase nuclei of A. rostrata , A. scholaris and A. yunnanensis were observed to be the rod-shaped prochromosome type, the round prochromosome type and the complex chromocenter type respectively, and the prophase chromosome types of the 3 species were all the interstitial one . The karyotype formulas are as follow: 2n = 42 = 3M+ 21m+ 18sm( A. rostrata) , 2n = 42 = 14m+ 24sm+ 4st ( A. scholaris) and 2n = 42 = 5m+ 37sm ( A. yunnanensis ). Karyotype asymmetries are of type 2A in A. rostrata , 3A in A. scholaris and 3B in A. yunnanensis. Based on the results, combined with the evidence from comparative morphology and cytology, the systematic position and evolutionary trend of this genus were briefly discussed .

Key words: Alstonia

摘要： 研究了鸡骨常山属( Alstonia) 3 个种的核形态, 其中盆架树( A. rostrata) 的核型属首次报道, 3 个种的体细胞染色体数目均为2n = 42 , 且糖胶树( A. scholaris) 和鸡骨常山( A. yunnanensis) 的染色体数目同前人报道的2n = 44 不同。盆架树的间期核和有丝分裂前期染色体分别为棒状前染色体型和中间型, 核型公式为2n = 42 = 3M+ 21m + 18sm, 核型不对称性类型为2A 型。糖胶树的间期核和有丝分裂前期染色体分别为球状前染色体型和中间型, 核型公式为2n = 42 = 14m + 24sm + 4st, 核型不对称性类型为3A 型。鸡骨常山的间期核和有丝分裂前期染色体分别为复杂染色体中央粒型和中间型, 核型公式为2n = 42 = 5m +
37sm, 核型不对称性类型为3B 型。根据核形态结果, 结合形态学特征和已有的细胞学资料, 初步讨论了该属几个种的系统位置及演化趋势。

关键词: 鸡骨常山属, 核形态, 系统位置, 演化趋势FONT