Thirty-eight crosses between seven Fagopyrum species native to China were studied. Following normal pollination, there were very low inter-group crossabilities (only 0-3%) between five species in the large-achene group and two species (F. gracilipes and F. pleioramosum) in the small-achene group, and high (15-50%) within the large-achene group, i.e. F. esculentum, F. tataricum, F. zuogongense, F. pilus and F. megaspartanium. Crosses between various types of flowers (homostyle, heterostyle etc.) suggested that the intraspecific incompatibility also occurs in interspecific crosses. The hybrid seeds obtained from interspecific crosses all withered or shrivelled and lacked activity. Only one hybrid plant was obtained, tetraploid F. esculentum tetraploid F. zuogongense. The hybrid displayed anomalous behaviour at meiosis, pollen grain sterility and withering of achenes, confirming the genetic differences between F. esculentum and F. zuogongense. The results support the hypothesis that F. megaspartanium and F. pilus are the possible ancestors of cultivated buckwheat