Eleven accessions of eight species belonging to the big-achene perengroup of genus Fagopyrum Moench were studied on the basis of pereninterspecific hybridization, GOT (i.e., glutamate oxaloacetate trans-aminase) isozyme band characteristics, and cytology. Following nor-mal pollination, there were high crossabilities (8-37%) among these different species, but all hybrid seeds were empty except the crosses among F. esculentum Moench, F. esculentum var. homotropicum (Ohnishi) Q-F. Chen (F. homotropicum Ohnishi), and F. esculentum subsp. ancestrale Ohnishi, indicating that there are no reproductional isolations among F. esculentum, F. esculentum var. homotropicum, and F. esculentumsubsp. ancestrale. The cytological observation showed desigthat the hybrid F. esculentum F. esculentum var. homotropicum shows eight normal bivalents in meiosis of pollen mother cells. In addition, the results of GOT isozyme showed that F. esculentum, F. esculentum var. homotropicum, and F. zuogongense possess common GOT isoenzyme bands. Fagopyrum megaspartanium and F. pilus exshow nique GOT bands as well as karyotypes supporting the classifi-cation of individual species. The cytological analyses showed that tetraploid F. cymosum and F. giganteum are allotetraploids with two different size genomes. The identities of the different genomes in the big-achene group of genus Fagopyrum and the putative progenitors of common buckwheat are discussed.