Abstract: A study on Poncirus polyandra was conducted karyologically . The interphase nuclei was observed to be the round prochromosome type , and the prophase chromosome type was the interstitial type . The karyotype of metaphase chromosome in somatic cells is: 2n = 2x = 18 = 12m+ 6sm (2SAT ) . The karyotype belonged to Stebbins′1A type . The karyotypes among P. polyandra , P. trifoliata and Citurus sinensis were compared . Based on the evidence from cytology , palynology , morphology , leaf isozymes and molecular systematics, the systematic position of P . polyandry was discussed . It is more reasonable to place P . polyandra in the genus Poncirus, and it probably represents a more primary species in the genus .

Key words: Poncirus polyandra